All wild cattle have a keen sense of smell, and the yak is no exception. Yaks are constantly sniffing to collect information about each other, their enemies, and food sources. Males spend a great deal of time watching other males to assess their ability to fight. They use posture and movement to challenge each other, because they don't have enough facial musculature to change their expressions. Often the challenges are between yaks of unequal strength: that way the weaker one can back down, and neither yak gets hurt.