a similar thing happened to me. i was 10 and i was in one of the stalls reading the graffitti (i know it sounds stupid but i was bored during class so i asked to go to the bathroom) when this girl comes in, thinking she the only one there, and she's taking a shit and she makes sounds like she's really trying to force it out. once she leaves, i freakin start to burst into laughter! tears were coming out of my eyes cuz that was so funny! the girl didn't even fuckin know i was there!