A few days ago, Max discovered his bellybutton.
We try to give him his "naked time" (diaper only) for 30 minutes or so every night before he goes to bed. He usually runs amok and tends to be even goofier when he isn't confined in his clothes. He started to bend forward, resting his head on the ground, twisting himself around in lots of uncomfortable looking positions. We figured he was just being strange (not uncommon). We realized he was trying to see his bellybutton.
Yesterday I asked him "where his belly button was". He looked down and started to tug at his shirt, a onesie, which he couldn't get off. He became quite frustrated. I think he believes that when he has a shirt on, he has no bellybutton.
17 months old, and never noticed it before. It's amazing all that he observes, and learns, and some of the things that he hasn't.