My dog, the illness psychic

According to researchers who study canine cognition, it’s usually not just pet owners’ imaginations. Pups really do know when their humans are having a rough time, and they use a rich variety of signals to figure it out. Not only can your pet tell when you have the sniffles, but domestic dogs have shown an aptitude for detecting both much more minute mood fluctuations and far more serious physical conditions.

“Dogs are preternaturally sensitive to changes in their people,” says Alexandra Horowitz, the head of the Horowitz Dog Cognition Lab at Barnard College. “If a person is infected with a virus or bacteria, they will smell different.” Some illnesses change a person’s odor so profoundly that even other people can notice it, but dogs are able to smell changes in their people that would escape human senses, or that are so early-on that the sick person barely feels any different. That’s because dogs’ have exponentially more powerful senses of smell than humans: They can have as many as 300 million olfactory receptors in their noses, as opposed to a paltry 6 million for the average person.

Researchers have also found that a person’s mood, which can be an indicator of a larger illness, triggers a dog’s sense of smell, too. Human emotions manifest physically in chemosignals what are emitted by the body, and dogs are adept at deciphering those changes.