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. Which one of the following, if true, most helps to explain the information about how often threat gestures are accompanied by physical attacks? ["Chimpanzees often respond to other chimpanzees' threat gestures with threat gestures of their own.", 'The chimpanzees that most often make threat gestures are the ones that least often initiate physical attacks.', 'Making threat gestures helps chimpanzees vent aggressive feelings and thereby avoid physical aggression.', 'Threat gestures and physical attacks are not the only means by which chimpanzees display aggression.']