This is a very interesting set of observations. At the time I wrote Beethoven's Anvil it seemed as though tight inter-individual synchronization was relatively rare. It'll be interesting to see how this line of investigation unfolds.
Yasuo Nagasaka, Zenas C. Chao, Naomi Hasegawa, Tomonori Notoya & Naotaka FujiiScientific Reports 3, Article number: 1151 doi:10.1038/srep01151Received 13 September 2012 Accepted 07 January 2013 Published 28 January 2013Abstracts: Humans show spontaneous synchronization of movements during social interactions; this coordination has been shown to facilitate smooth communication. Although human studies exploring spontaneous synchronization are increasing in number, little is known about this phenomenon in other species. In this study, we examined spontaneous behavioural synchronization between monkeys in a laboratory setting. Synchronization was quantified by changes in button-pressing behaviour while pairs of monkeys were facing one another. Synchronization between the monkeys was duly observed and it was participant-partner dependent. Further tests confirmed that the speed of button pressing changed to harmonic or sub-harmonic levels in relation to the partner's speed. In addition, the visual information from the partner induced a higher degree of synchronization than auditory information. This study establishes advanced tasks for testing social coordination in monkeys, and illustrates ways in which monkeys coordinate their actions to establish synchronization.