When chimpanzees become angry at other chimpanzees, they often engage in what primatologists call threat gestures: grunting, spitting, or making abrupt, upsweeping arm movements  Chimpanzees also sometimes attack other chimpanzees out of anger  However, when they do attack, they almost never take time to make threat gestures first
And, conversely, threat gestures are rarely followed by physical attacks
Chimpanzees often respond to other chimpanzees' threat gestures with threat gestures of their own.