Cats rub against people and places to deposit saliva and secretions from three glands on the head. These deposits send a message to other cats: You are part of their territory. It may be like posting a “no trespassing” sign.
In the wild, creatures from lowly mice to lumbering bears and fleet-footed deer mark the trees and ground with semiochemicals. “Semio” is from Greek, meaning a “sign,” and mammalian signs are read with considerable interest. They often define territories, but their particular mixture of 50 or more compounds may even identify an individual animal, as a name or Social Security number identifies us.
In the case of deer, the meaning of scents can be quite complex, advertising a buck’s status in the herd, triggering the reproductive cycle in females and perhaps even stemming the sexual drive in bucks of lower status.
Most mammals have much better olfaction than humans – dogs and their wild kin have up to a million times more scent receptors than we do.
So remember when you take Fido for a walk: Those leaves and twigs he spends so much time sniffing could be his version of reading the local newspaper.