Humans have a tendency to spontaneously synchronize their movements. For example, the footsteps of two friends walking together may synchronize, although neither individual is consciously aware that it is happening. Similarly, the clapping hands of an audience will naturally fall into synch. Although this type of synchronous body movement has been observed widely, its neurological mechanism and its role in social interactions remain obscure. A new study, led by cognitive neuroscientists at the California Institute of Technology (Caltech), has found that body-movement synchronization between two participants increases following a short session of cooperative training, suggesting that our ability to synchronize body movements is a measurable indicator of social interaction.