In the last few minutes of Close Encounters of the Third Kind, the French ufologist Claud Lacombe does 5 hand gestures in the presence of a single alien. The gestures are supposed to represent the 5 tones played throughout the movie. The alien does some similar hand gestures in return.
I'm very curious if, within the movie, the alien was supposed to know that the hand movements represented the musical theme. Also, why would the alien have repeated those particular gestures, since humans were doing all kinds of motions with their hands prior to that? (To be fair, everyone except Lacombe was completely still during this exchange.)