"How did you get poopy on your foot?"

I just asked my son this question, not even 10 minutes ago. The reason it is so perplexing and a bit disturbing is that he was on the toilet at the time. I still have no concrete answer. He could not articulate how it got there, all he said was something like 'yeah, I got poopy on my foot' and 'there's poopy in the toilet and it got on my foot.' Yeah, but how??? How does a child do something like that, while still seated, and have it be on the back of his foot, near the ankle?! I don't get it, I just don't. That's probably best. When I told my husband he just said 'ew.' What else is there to say?