How does Fido do it? It’s no secret that dogs have an acute and sophisticated sense of smell, and the scientists believe the canines are picking up on very subtle changes in certain volatile organic compounds in the breath, which may change when cancer is present. (In the study, patients exhaled into glass tubes filled with odor-capturing fleece, and the dogs were given these to sniff.)

The dogs were also able to distinguish between patients with lung cancer and those with chronic obstructive pulmonary disease, as well as between smokers and nonsmokers.