Poopy on the Potty (or "the brown one")

Last night while in the bathtub, Jonah says, "there's a tube in your tushy". I asked if he had to poop and he said yes so I put him on the potty and he sat and made on there! He was all excited to flush it down the big toilet afterward.
Tonight, as I was changing his diaper before bedtime, he said he wanted to go poopy again on the potty so I took him on it. He made a pee but not a poop. He got off the toilet and looked inside. He said, "Where's the brown one?" I explained to him that only pee pee came out and it's yellow, not brown. He seemed surprised. He kept saying that there was a whole in his penis. I explained it's where the pee comes out. Fascinated.