A funny thing in Primary today

Today in Primary, the chorister told the kids that for every song they sang well, she would cut a piece off of one of the teacher's ties. Of course, he knew about this before so he could wear a tie he didn't care about. The kids really got into it and sang so well the teacher's tie was gone by the end of singing time. At one point, Sam yelled out "Cut off his pants!" The kids went nuts laughing and the adults couldn't hold it in either. It was a really fun time. That isn't the first time Sam has yelled out a funny comment in Primary but it was the funniest comment so far. There is nothing I can do to stop him from saying these things because I don't know what is in his head and coming out his mouth and I am just as helpless to laughter as everyone else. What's a mom to do?