What’s It Like to Be a Rat?

David Paul, Museums Victoria, CC BY 4.0.

David Paul, Museums Victoria, CC BY 4.0.

Rats experience the world quite differently from us. While we may never know what their life is really like, we can get some idea by seeing what their senses are like.

While most of us rely primarily on our sense of sight, rats are far beyond legally blind. What they see at 20 feet (6 m) is as detailed as what we normally see at 2,000 feet or 0.4 miles (600 m), though that’s probably not surprising since they can’t see anything in focus more than six inches (15 cm) in front of their noses. They mainly rely on their whiskers and sense of smell. This is why they run along baseboards and walls. It’s so they don’t get lost. They’ll rarely venture into the middle of a room. On the other hand, if their vision is like that of mice, then they can see the dimmest shadows in the lowest light.[1]

Their eyes are completely independent and look in different directions, though wherever they look, they constantly have the space above them in view with both eyes, watching for predators. When they lower their heads, their eyes move up toward the back of their heads, and when they raise their heads, their eyes move forward like they’re cross-eyed in order to keep the space above them in view. Unlike us, the two images aren’t fused, so they have no stereovision.

The lower half of their vision is sharper than the upper half. The upper half can see ultraviolet light, making it easier for them to spot predators, while the lower half can see green, otherwise everything is in shades of gray. They recognize objects by looking for the typical characteristics that are the least likely to change when looking at that object from another point-of-view.

Smell is a rat’s primary sense, but their sniffing is coordinated with sweeping their whiskers back and forth up to 12 times a second, so they smell and feel their way around. It’s thought their whiskers feel to them much like the touch of our fingers feel to us. It enables them to feel an object’s properties, such as its size, shape, texture, distance, orientation, and motion. Each whisker acts like an antenna and amplifies the signal from its tip a thousand-fold. The data from each whisker is combined by the rat’s brain to form a seamless view of the world, much as our brains do with sight.

Scents entering each nostril are processed separately, enabling them to smell in stereo. They can locate the source of a scent with just one or two sniffs. So far we’ve discovered that moles and ants also have this ability.

Small rodents, such as rats and hamsters, communicate with each other using a series of rapid chirps in the ultrasonic range—well above our ability to hear them. At close range these chirps can be as loud as a jackhammer, but because of their high frequency, the sounds are directional and fade quickly with distance—within a few yards—so while a nearby companion can easily hear it, a cat farther away or in another room might not.

We can hear frequencies of 64 hertz to 20,000 hertz, while dogs hear from 40 to 45,000 Hz, cats from 45 to 64,000 Hz, rats from 200 to 95,000 Hz, bats from 20 to 200,000 Hz, chickens from 10 to 12,000 Hz, for whales it’s somewhere between 16 to 200,000 Hz depending on the species, and T-Rexes primarily heard sounds in the low range, much like their closest descendants, chickens.

So cats can hear some of a rat’s lower-end chirps, but are just as likely to see or smell them. But a rat’s repertoire is larger than just chirps, and includes singing songs to each other on various occasions.

Practically Blind

Armadillos, sloths, and anteaters have horrible vision. They can only see in black and white, and are pretty much blind in daylight. They’re also unable to focus their eyes.

Once in the woods of Texas I had an armadillo walk right up to me without knowing I was there. When I made a sound, it took off running as fast as it could in the opposite direction. Perhaps this is a good strategy for them, but since they can’t really see where they’re going, they sometimes run right into a tree. Fortunately they’re covered in armor.

Toads, possums, and rhinoceroses are also extremely nearsighted. Rhinos sometimes charge at large rocks, repeatedly. And they can’t tell a human from a tree at fifteen feet. A toad mainly needs to see prey which is within shot of its tongue—a couple of inches away. I’ve walked right up to cane toads too, but they can see movement and a shadowy outline coming towards them.

 

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[1] Aalto University, "The limits of vision: Seeing shadows in the dark: A dedicated neural circuit in the retina detects shadows even in near-complete darkness", ScienceDaily, May 23, 2022, https://www.sciencedaily.com/releases/2022/05/220523115459.htm, citing Johan Westö, Nataliia Martyniuk, Sanna Koskela, Tuomas Turunen, Santtu Pentikäinen, and Petri Ala-Laurila, “Retinal OFF ganglion cells allow detection of quantal shadows at starlight”, Current Biology, 2022, https://doi.org/10.1016/j.cub.2022.04.092.

Sense of Smell in Dogs and Cats

Salem Eames, CC BY-SA 2.0 (adjusted).

The vision of wolves is similar to that of dogs—not that great, although they can see farther—so they rely on their sense of smell to locate their prey up to four-and-a-half miles away. Likewise, dogs have an extremely sensitive sense of smell. That’s why we use dogs, such as bloodhounds, to track down people or find narcotics and explosives. It appears they can smell our emotions, in addition to seeing and hearing evidence of them. But their sense of smell is much more sensitive than that. Archeologists discovered cadaver dogs can find ancient graves that are at least 2,700 years old.[1]

Dogs’ noses have a 100,000 times increased sensitivity than ours. They can detect a diluted chemical that would be the equivalent of a pinch of sugar mixed into a billion cups of tea.[2] When we smell pizza, that’s what we smell, but it’s said dogs smell each individual ingredient. Like cats looking at a brick wall, we don’t sense the detail. Interestingly their olfactory sense routes some information to their occipital lobe, raising the possibility that dogs can see smells,[3] perhaps like people with smell-visual synesthesia.

Tests done at the Istituto Clinico Humanitas in Italy using over 600 patients have shown that dogs can even smell certain forms of cancer—including melanoma, and lung, colon, and ovarian cancers—with a 98% success rate.[4] Sometimes dogs are more accurate than the usual lab tests and have fewer false positives. Scientists have also trained bees, ants, and fruit flies to detect cancer, along with using giant African pouch rats to identify tuberculosis.

This talent might not be as difficult as it sounds. Some sensitive nurses say they can also smell diseases. They say cancer has an earthy vegetable scent, while Parkinson’s disease smells musty, Alzheimer’s smells of vanilla, and typhoid is like freshly baked bread. But not all are that pleasant. Liver failure is said to smell of raw fish and yellow fever like a butcher’s shop. Some even say they can smell impending death.

There’s an anecdote reported in The New England Journal of Medicine of a cat named Oscar who lived at a nursing home in Provincetown, Rhode Island, that didn’t like to interact with people, except during the last couple of hours before one of the residents died. Without fail he’d jump on the patient’s bed and lie down by them, purring until the person passed away. Then he’d get up and leave, returning to his aloof existence. He was even better than the doctors at predicting deaths, getting it right more than 25 times. It got so that when Oscar jumped on someone’s bed, the nurses immediately notified the family.[5]

Cats and dogs have a second olfactory organ between the back of their nostrils and the roof of their mouths called the Jacobson’s organ. Here cats beat out dogs with this second nose—having 30 receptors compared to the nine in dogs. When cats pull up their upper lip in a grimace, exposing their upper teeth, they are using this unusual sense, which is thought to be somewhere between smell and taste. Usually it means they’ve smelled another cat.

Snakes also have this sense, waving their tongues in the air or water, before sucking it back in and transferring whatever it picks up through ducts to their Jacobson’s organ. Whichever side of their forked tongue picks up the strongest scent is likely the direction the smell came from so they head towards it for prey and away if they smell danger.

While dogs are excellent sniffers, the animals that appear to have the best sense of smell of all, are elephants.

Cats can’t taste sugar or salt. They lost both tastes through genetic mutations. Sweetness is primarily of importance to animals that eat fruits and berries. Carnivores don’t really need it, and of all the carnivores, cats are the most devoted to eating meat. Tigers and cheetahs also can’t taste sugar. Dogs, on the other hand, have a bit more varied diet and there are indications they can still taste sweetness.[6]

Of course, cats are not the only ones who taste things differently. For rats, mice and some monkeys, artificial sweeteners do not taste sweet, though, interestingly, fruit flies sense sweetness very much as humans do. That is, most humans. Personally, artificial sweeteners taste incredibly horrible to me, my wife, and daughter. They are a bit sweet, but they have a metallic oiliness that sticks to our tongues and just won’t go away no matter how hard we try to get rid of it or cover it up. Perhaps the way we perceive sweetness is more like that of some monkeys, than like that of fruit flies, but we seem to be an exception to that rule. The popularity of these sweeteners indicates they don’t taste like a toxic chemical to most people.

Cats aren’t the only ones who’ve lost some of the five or more tastes. Some birds, such as chickens, can’t taste sweetness either. Penguins, dolphins, and sea lions can only taste salty and sour, partly because some tastes—sweet, bitter, and savory—don’t work well when it’s cold, but also because they usually swallow their food whole.

Catnip

Catnip has an unusual effect on cats. Both catnip (Nepeta cataria) and silver vine (Actinidia polygama) contain a scent that causes a release of their brains’ natural opiates. Their eyes widen, they roll around in obvious pleasure, and they start drooling. It also seems to give them temporary pain relief. The effect lasts for about ten minutes, but not all cats are susceptible to it. About a fourth of cats lack the gene for it, and young kittens don’t like it. But it does affect the larger cats—lions, leopards, jaguars, and lynxes—in much the same way as most house cats.[7]

 

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[1] Joshua Rapp Learn, “Dogs show a nose for archaeology by sniffing out 3,000 year old tombs”, The Guardian, October 24. 2019, https://www.theguardian.com/science/2019/oct/24/dogs-show-nose-archaeology-sniffing-out-ancient-tombs.

And Cat Warren, “When Cadaver Dogs Pick Up a Scent, Archaeologists Find Where to Dig”, New York Times, May 19, 2020, https://nyti.ms/3cLlE5p.

[2] “A nose with an attitude” side box in Anthony King, “The Nose Knows”, New Scientist, August 24, 2013, pp. 40-43, and as “How to train a canine conservationist”, August 21, 2013, https://www.newscientist.com/article/dn24047-how-to-train-a-canine-conservationist/.

[3] Cornell University, "New links found between dogs' smell and vision," ScienceDaily, July 18, 2022, https://www.sciencedaily.com/releases/2022/07/220718181030.htm, citing Erica F. Andrews, Raluca Pascalau, Alexandra Horowitz, Gillian M. Lawrence, and Philippa J. Johnson, "Extensive Connections of the Canine Olfactory Pathway Revealed by Tractography and Dissection", The Journal of Neuroscience, 2022, JN-RM-2355-21, https://www.jneurosci.org/content/42/33/6392, https://doi.org/10.1523/JNEUROSCI.2355-21.2022.

[4] Carl Engelking, “Dogs Sniff Out Prostate Cancer With 98 Percent Accuracy”, Discover Magazine, May 19, 2014, https://www.discovermagazine.com/the-sciences/dogs-sniff-out-prostate-cancer-with-98-percent-accuracy.

And Experimental Biology, “Study shows dogs can accurately sniff out cancer in blood: Canine cancer detection could lead to new noninvasive, inexpensive ways to detect cancer.”, ScienceDaily, April 8, 2019, https://www.sciencedaily.com/releases/2019/04/190408114304.htm.

[5] David M. Dosa, “A Day in the Life of Oscar the Cat”, The New England Journal of Medicine, 357, July 26, 2007, pp. 328-329, https://www.nejm.org/doi/full/10.1056/NEJMp078108, https://doi.org/10.1056/NEJMp078108.

[6] “The Chemosensory World of Pets”, The Monell Connection newsletter, Fall 2000, pp. 1, 5, http://www.monell.org/Newsletters/Monell_Fall00.pdf.

And “Defective sweet taste receptor gene shapes cat cuisine”, press release, Monell Chemical Senses Center, http://www.monell.org/files/news/cat_sweet_taste.pdf.

And Ed Yong, “A lack of taste – how dolphins, cats and other meat-eaters lost their sweet tooth”, National Geographic, March 13, 2012, http://phenomena.nationalgeographic.com/2012/03/13/sugar-sweet-taste-cats-dolphins-carnivores-genes.

[7] Sofia Moutinho, “Why cats are crazy for catnip”, Science, January 20, 2021, https://www.sciencemag.org/news/2021/01/why-cats-are-crazy-catnip, https://doi.org/10.1126/science.abg6551.

What’s It Like to Be a Cat?

 

© Elaine Molina Stephens, 2024.

“But do cats eat bats, I wonder?” And here Alice began to get rather sleepy, and went on saying to herself, in a dreamy sort of way, “Do cats eat bats? Do cats eat bats?” and sometimes “Do bats eat cats?” for, you see, as she couldn’t answer either question, it didn’t much matter which way she put it.[…] did you ever eat a bat?

—Alice in Alice’s Adventures in Wonderland, 1865

Imagine you’re an animal. That shouldn’t be hard since you are an animal. So to be more accurate, imagine you’re another type of animal—a cat.

Back in 1974 philosopher Thomas Nagel wrote his well-known essay, “What is It Like to Be a Bat?”[1] Philosophers and scientists have had many interesting discussions over it ever since. In his argument against reductionism, he insisted that it’s impossible for us to know what it’s like to experience the world as a bat, since their sense of echolocation is so alien to us. He has a point, but while we may never know what a bat’s view of the world looks like after its brain processes the data from its senses, we have learned a lot about echolocation and how a bat’s senses work, thus we’ve gained insight into what their world might be like.

We can’t yet know what it’s like to be another animal, just as we can’t know what it’s like to be another person, but I’d like to go over a few things we’ve discovered, mostly since Nagel wrote his essay. This won’t deal with qualia—the subjective, conscious experience—but I think it’s a step forward in understanding what these creatures experience. It may not be long before we can accomplish this better with immersive virtual reality. Nagel used bats as an example, but he intended his argument to apply to all animals, so I’d like to look at a few others that we’re a bit more familiar with.

Dogs and cats can’t see nearly as well as us. Both are red-green color blind, so to them the world is in washed-out shades of yellow and violet, although some experts think cats only see in violets and grays. Either way, this means green pretty much looks yellowish white to them and red looks gray to yellowish gray. If you throw a red ball into grass, your dog will have to search for it mostly by its shape. So get your dog a blue ball. In addition, as their eyes are three feet (1 m) or less from the ground, objects like long grass can block much of their view.

One recent study by researchers in Hungary and Mexico suggests that dogs don’t really notice the differences in people’s faces, since unlike us, they don’t have a specific area in their brains for processing faces. They mainly recognize you by your voice, smell, or movements, probably with a bit of help by your clothing or other distinguishing features.

Dogs and cats have a wider field of view than we do, but with dogs there’s less overlap of their eyes, so less of their view is three-dimensional. On the other hand, dogs and cats have a visual streak instead of a fovea, so their peripheral vision is better since the streak puts a greater length of the horizon in focus, whereas our fovea is just a spot.

They also see less contrast than we do. Because they have more rod—receptors that detect black and white, providing night vision—than us, everything appears lighter and they’re better at detecting motion. They’re particularly good at detecting objects moving at certain speeds, but slow moving objects may look stationary to them and they’re not as good as us at seeing motion in the bright light of day, although dogs can see a little better during the day than cats.

But other vertebrates, such as fish and reptiles, may have color vision even better than ours, with four color receptors. Birds and turtles can see more shades of red and ultraviolet than us because their red receptors peak closer to infrared and they have an ultraviolet receptor. This would mean birds, fish, and reptiles have day vision; dogs, cats and most mammals have night vision; while we fall in the middle.[2]

So throwing a ball that is red for your dog to chase will increase the chance he or she will lose it, but you can use it to play fetch with a turtle, especially since turtles are attracted to red, but that probably won’t be a very exciting game.

Both dogs and turtles see much better than us at night, but it’s essentially in black and white. They can also see ultraviolet light to some degree, which helps them with night vision. Dogs, cats, owls, deer, raccoons, and some other mammals have a reflective layer of tissue behind their retinas to help them see better in the dark. Photons that pass by their receptors are reflected back through the retina giving them a second chance at being received. This is why their eyes glow in the dark when you shine a light on them.

On the down side, because the layer scatters light, these animals’ visual acuity is much less than ours. Cats don’t see well close up or far away—it’s more in the midrange, although outdoor cats can see well slightly farther away, while indoor cats can see better a bit closer. This doesn’t mean everything is fuzzy, it’s likely if they look at a brick wall they’ll clearly see the wall—they just won’t see the bricks. What they see will lack detail.

It’s thought that cats and dogs can’t adjust the focus of their eyes to different distances as well as we can, and that ten inches (25 cm) might be the maximum for cats and twice that for dogs, so only things in a narrow distance would be in focus. Cats can’t focus on anything that’s less than a foot (30 cm) in front of them, so they rely on their whiskers to sense those things. Of course, many people have a similar problem and rely on their reading glasses.

If you have 20/20 vision, what you can see at between 50 and 100 feet (15-30 m) is about as focused as what most dogs see at 20 feet (6 m). Certain breeds—such as Labradors, Australian Shepherds, and Alaskan Malamutes—were bred for better eyesight and can see almost as well as us, while others—Toy Poodles, Collies, and Rottweilers—are nearsighted.

For cats, what they see at 20 feet (6 m) would be about as clear as what we see at between 100 and 200 feet (30 to 60 m). In other words, cats would be considered legally blind and dogs are close. And both cats and dogs can’t see anything you put under their nose, since their nose is in the way. We don’t have that problem.

I find it interesting that the seeing-eye dogs used to assist blind people are not that great at seeing. Fortunately their other senses are much keener than ours.

Why Cats and Dogs are Color Blind

Vision originally evolved in the ocean, which is probably why we see the spectrum of light that we do. Electromagnet radiation just above ultraviolet and below red is absorbed by water, so it’s likely vision evolved to make use of what was left. The common ancestor of reptiles, birds, mammals, and dinosaurs probably had good color vision, as many fish do.

As dinosaurs evolved to be large successful predators, they came to dominate the daylight hours. Their cousins, the reptile-like proto-mammals, found they could better avoid becoming dinosaur kibble by foraging at night. Throughout the reign of the dinosaurs, our ancient ancestors were nocturnal, so their vision evolved to better see at night by increasing their rods and losing two cones—red and ultraviolet—reducing them to the two remaining cones that almost all mammals still have. Birds and reptiles still have three or four of them.

Millions of years ago dinosaurs were the monsters that drove mammals to forage at night. Now it’s happening again with many animals being forced to forage at night, only this time we’re the monsters driving them to it.

When all the dinosaurs were wiped out, except for those who would evolve into birds, mammals returned to living in the daylight. Somewhere along the line primates regained their red receptor, restoring the tri-color vision that apes (including us) and Old World monkeys have today, but which New World monkeys don’t, except for Howler monkeys who regained it on their own. These are the only animals in the world who see colors the way we do. And this is why most mammals, including dogs and cats, have poor color vision.

Mammals and their ancestors went from day to night vision, and have returned to mostly day vision. Humans have progressed further on this path than dogs and cats. Similarly, the reptilian ancestors of crocodiles, alligators, and turtles moved from water to living on land, but later returned to water. While on land their eyes adjusted to seeing through air, which is very different from seeing through water, mainly because of refraction, or the bending of light when it hits water. Turtles have adjusted, so they can see fine in air and water, but crocodiles haven’t. They still have trouble seeing underwater, just as we do.

 

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Endnotes

[1] Thomas Nagel, “What is It Like to Be a Bat?”, The Philosophical Review, vol. 83, no. 4, October 1974, pp. 435-450, https://www.jstor.org/stable/2183914.

[2] Richard Dawkins, The Ancestor’s Tale: A Pilgrimage to the Dawn of Life, Boston, MA: Houghton Mifflin, 2004.

And Evan Thompson, “Colour Vision, Evolution, and Perceptual Content”, Synthese, no. 104, 1995, pp. 1-32, http://individual.utoronto.ca/evant/ColourSynthese95.pdf.

And University of Texas at Austin, "New study shows effects of prehistoric nocturnal life on mammalian vision", ScienceDaily, October 31, 2012, http://www.sciencedaily.com/releases/2012/10/121031161025.htm, citing M.I. Hall, J.M. Kamilar, and E.C. Kirk, "Eye shape and the nocturnal bottleneck of mammals", Proceedings of the Royal Society B: Biological Sciences, 2012, https://royalsocietypublishing.org/doi/10.1098/rspb.2012.2258, https://doi.org/10.1098/rspb.2012.2258.

Also Veronique Greenwood, “Eye of the Beholder”, New Scientist, April 18, 2015, pp. 40-43, and as “Eye of the beholder: How colour vision made us human”, April 16, 2015, https://www.newscientist.com/article/mg22630170-400-eye-of-the-beholder-how-colour-vision-made-us-human.