I was in the car with my younger cousins one day, who were 7 and 5 at the time. The 7 year old was saying to the other what makes a car run and what makes certain things do what they do and then he decided to say what makes the boogies come out of your nose.

His sister replied, "My fingers".

Needless to say it was a classic moment that we all got a good laugh out of.