When people move together, as they dance, march or flirt, it increases affiliation between them. But what about ‘moving together’ produces affiliation: the movements themselves, or the social context of moving ‘together’? We instructed pairs of participants to listen to music and move their arms or legs according to shapes appearing on screen. They either carried out the same movements, or when one moved their arms the other moved their legs. They either saw shapes on one laptop, or each had their own laptop. Surprisingly, participants did not like each other more if they carried out the same movements, but affiliation did increase if they danced looking at the same screen. Rather than their movements, instructions, intentions or perceptual experiences, here it is the social context of the actions that produces affiliation, a surprising finding that is not easily accounted for by the dominant theories of mimicry and behavioural synchrony.