Five senses

This week at preschool we are studying the five senses. During a discussion at circle time yesterday, the kids were talking about each sense. I was filling snack cups up at the sink and listening to what was going on behind me. When Miss Susan asked the kids, "what are some things we can hear?",one of the kids let a BIG toot rip! It was like it was planned. I just lost it, I couldn't help it. The kids (and I )were hysterical and poor Miss Susan had to maintain her composure and try to continue with the lesson. Why is farting so funny?