Recently, we have seen a surge of interest in identifying possible evolutionary links between primate facial communication and human speech (for example [1]). One suggestion is that primate ‘lip-smacking’ — a non-vocal, rhythmic movement of lips usually given in conjunction with affiliative behavior — may have been a precursor to speech [1]. This idea arose because lip-smacking shares several production features with human speech that the vocalizations of non-human primates lack, most notably a 3–8 Hz rhythm [1]. Evidence that non-human primates are indeed able to vocalize while simultaneously producing rhythmic facial movements would lend initial, but important, support to...