Earliest = not much before I turned 2.
I was in my crib, bored as hell. Left with nothing else to examine that I had not already examined a thousand times before, I started wondering about the precise things which were normally under my diaper.
I discovered I had... a third hole. I remember.
*feels around* Here's where the pee must come out.
*feels around* Aha, that's where the poop comes from.
*feels around* ... what is THIS, between the two?! Another hole! ...was this normal? Was I sick? Was I going to die?
I thought of death and the pain which by my understanding would be a part of it. (My parents did not shelter me from such things, even at that age.) Would I be like those dirty, sad little mounds of fur I saw on the sides of the roads sometimes? Or maybe I'd be like those old people in the hospitals, who never come home?
I was very scared lil.
I remember asking my mother about it later that day... it took her quite some time to stop laughing and answer me, as I recall.