Harry: (at top of voice, no matter where you are) A POO! A POO!
Us: (quietly) Oh, you did a poo?
Harry: YES!! (points at bum) RIGHT THERE!!!!
or
Harry: (at top of voice, no matter where you are) A POO! A POO!
Us: (quietly) Oh, you did a poo?
Harry: NO!! ITS GAS!!!