There is a certain laugh people laugh when have a realization which will alter everything they previously thought. Like when Charlton Heston sees the Statue of Liberty while riding away from some very corrupt monkeys or when Harper heard that the leader of the opposition did not have long to live. The laugh belongs to the person who now knows something about what’s going on or what’s going to go on.
It was only last year I considered that the Paul McCartney song “Why don’t we do it in the road?” might be about screwing. Since I started listening to it when I was a little boy I just thought it was a philosophical statement as in we could do anything in the middle of the road (which may also be what he wanted to say)….but when I considered last year that it’s just about fucking, I’m ashamed to say I started to laugh like Harper.