Consider that chimpanzees utter laughlike sounds when they are being chased by
other chimps, and as with human children, the one being chased is the one
who laughs.
Interestingly, they also found that the better throwing
chimps didn't appear to posses any more physical prowess than
other chimps, which the researchers suggest means that throwing didn't develop as a means of hunting, but as a form of communication within groups, i.e. throwing stuff at someone else became a form of self expression, which is clearly evident to anyone
who has ever been targeted by a
chimp locked up in a zoo.