Pigs can also use odor from urine and the facial glands to identify other pigs, and even pigs who are unable to see are able to recognize other individuals in their group, indicating the strength of their other senses. Olfaction plays an important role in a sow's maternal behavior, for example, by helping to form strong bonds with her offspring.
Pigs also communicate by scent-marking prominent features in their home ranges. As they are not very territorial, however, the purpose of scent-marking might be to establish group cohesion, rather than to mark territory. Sometimes pigs will urinate to show their displeasure with you (or be a jerk) and this is their way of communicating with you.
The nasal disc on a pig's snout, while rigid enough to be used for digging, has numerous sensory receptors. In addition to being useful as a fine and powerful tool for manipulating objects, the extensive innervation in the snout provides pigs with an extremely well-developed sense of smell.
Indeed, olfactory signals play an important role in communication, and pigs can communicate by releasing chemicals in their saliva and urine called pheromones. In an impressive example of symbiosis and interspecies communication, truffles developed the capacity to produce an allomone that mimics boar testosterone. The sow, upon finding the scent, uses her special snout to dig out the truffle, thus disseminating its fungal spores and enjoying a treat for her efforts.
A pigs snout resembles an upside down heart.
Pigs can smell roots and tubers that are deep underground—a unique skill that has been exploited since the ancient Babylonian period to find truffles, a subterranean fungus that grows around the roots of oak trees and is highly prized by gourmet chefs. This practice was ceased and outlawed in some countries when the pigs were damaging the delicate parts of the truffles causing the prices to soar.