"It's a mystery!"

Then there's Thomas...

The night before I left Annapolis, we were having dinner at Grandmom's, and Thomas asked me to take him to the bathroom to pee. So I take him in, and he lifts the toilet lid and continues holding it while he starts to pee. He dropped it, and he goes
"Oops! It almost fell on my peanut!"
"Oh Thomas, that's your penIS. A peanut it a food, like peanut butter?" and he goes
"No, it's a peanut. Mommy said it's my peanut."
"Hmmm..." I say, not feeling like arguing with a 3 year old.
He shrugs and says, "It's a mystery!"