A geography class...
Teacher goes on and on about bird droppings. 'bird droppings are a huge industry....bird droppings blah bird droppings blahblah'
and all is fine and boring till somebody raises their hand....
"Ma'am, but what.." (and the tone mind you is like the next big philosophical question just about to be revealed) "but what....do birds drop?"

(yes it's a true story)