My friend's little girl was having tummy troubles. She went to the doctor and found out that she was severely constipated. They told her to put her on laxatives to help her move thing along.
The laxatives worked a little too well and she ended up with the runs.
She didn't understand what they were and this conversation ensued:
"When you go to the bathroom and you poop you need to tell me." her mom said.
"I didn't go poop. I only went pee." she replied.
"No, you did go poop. It's just liquidy and sounds like pee. It's called having diarrhea." her mom informed her.
Later, as she and her brother were playing she got up and ran as fast as she could to the bathroom. Barely making it onto the toilet in time she yelled to her mom, "Yep! It's bacteria again!"