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| 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, .
[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, 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, 10.1126/science.abg6551.
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