Well, this took a terrifying turn. Let's hope he doesn't learn all the wrong things to do, just in case he's got other scarier alien powers. His views on overpopulation are already worrying.
But I get it, from what he saw that day that looks like the appropriate reaction to someone falling. He just hasn't learned to differentiate a silly fall from a serious one. Also I'm not sure if he understands concepts of pain and danger like we do.
ahh i get it now... he's choosing to laugh because he's been seeing that one guy fall a lot and everyone laughed... but when the girl fell, he also thought he was supposed to laugh too since he seem to not be able to tell apart a serious and a non-serious/comedic fall. But jesus christ, where did he learn to laugh like a sadist