Anal Phase

My kids have this obsession with poop right now. So much so, that it is said at least a hundred times a day followed by unstoppable giggles.
Imagine this...A nice quiet drive back home, adult conversation, while the kids have their headsets on watching "Bee Movie" and Grant half sleeps watching in silence. This goes on for a wonderful 45 minutes. So peaceful to have them awake, but totally silent.
All of a sudden, they both burst out in giggles yelling "Poo Water! Poo Water! Ha! Ha! Ha!..." It was quite funny, especially since they didn't realize how loud they were with headsets on. Then, when the laughter subsided, complete silence for the rest of the drive home.
Does anything else make my children laugh besides poop and pee? I am still trying to find it.