Occasionally fall occurs accidentally when branch breaks. Cf. leap down and fall. See video. drum Component of charging display. Goodall: Hit and/or kick tree trunks, especially those with buttresses. Often they grab the buttress with their hands and stamp on it with their feet. They may kick backwards with their feet or hit the trunk or buttress with their hands. Often a particular drumming tree triggers a drumming display and the individuals of a traveling group are likely to drum one after the other as they pass. Usually drumming is accompanied by the pant-hoot call, but sometimes drumming is without vocalization. Chimps at Gombe also pound on the walls of research buildings and on a barrel placed at the feeding area. Plooij Drum. Mahale chimpanzees do same. Drumming