Babies be all like, "Imma drop this, you gonna pick it up. Who you think's in charge, again?"
Object permanence. That's the scientific excuse that people use to explain why babies get such a kick out of dropping things from their high chairs. The theory is, babies' brains aren't mature enough to understand that dropping something out of the line of sight doesn't mean it has actually disappeared. If it did, that'd be a pretty cool trick!
The thing is, though, babies aren't dumb. We are. They know exactly what's going on. They keep dropping it because we keep picking it up! They turn to their little friends on play dates, wink and say, "Heh. Watch this." It's the same reason a dog chases a ball when you throw it. That dog's totally thinking, "Can you even believe this jackwad right now?"
It's cool, though. We aren't the ones pooping our pants or licking our butts, so as far as I can tell, we've still got a slight edge.