You've heard of flipping the bird; how about flipping the lip? When threatened, a gelada displays aggression through the "lip flip," an act of eversion in which they turn their upper lips inside out on their nostrils to reveal their gums and teeth. Despite a diet of mainly grass, they're equipped with large canines that are used as a sign of dominance. 📸: Agustin Valadez #FangFriday #Gelada #OldWorldMonkey #SanDiegoZoo