in succession. It is the typical sound given by an infant which cannot reach the nipple and wants to reestablish contact with the mother etc. Mahale infants hoo when begging for food, when wanting to return to mother after separation, and when seeking to mate with estrous female. Mothers also hoo when older infant does not return to her, often while playing overhead when she wants to leave. Hoo expresses frustration. Cf. whimper. Absent in bonobos? 5. See video. hook branch Sugiyama Branch-hauling, Whiten et al.s Branch-hook: Use branch to hook another branch. Present only at Bossou. Absent at Mahale. See Fig. 20. hoot Goodall: Roar pant hoot. Continuous low-pitched calls given only by highly aroused individuals, rarely by females. Always accompanied by a charging display. 5. hoot