How could so much come out of such a little body?

We had the biggest poo-splosion to date this morning:

All I can say, is thank goodness we were at home and I could put him right in the bathtub, clothes and all! He actually didn't mind the bath so much, I think because I confused him by not undressing him before I put him in. How can so much poo come out of one little body?? He has started going days at a time without going #2, but it seems like when he does go it is a doosey!