You stepped on what? 8.23.10

The girls had  friend over today. A 6 year old boy who loved the work Fart. Which is a word that my girls are not encouraged to say. But to make their friend feel at home they were using it freely. At one point a daughter (who will remain nameless) tripped and said "oops! I stepped on my F*RT!" What? How the heck did that happen?