Riddle

Aidyn in the bathtub the other night:

"Ok, Mama. Here's a riddle. What says 'boom, boom,' and has four legs, and [looking around the bathroom] a towel?"
"I don't know, Baby. What What says 'boom, boom,' and has four legs, and a towel?"
"I don't know Mama. That's why it's a riddle!"