Playing with Words

Often during a rhyming lesson things get a little sticky when the students start playing with words.  I have had a group of children start a rhyme train;  one starts with hawk, the next child adds knock, the third one rock and of course just as the principal walks in the fourth one excitedly calls out "cock".  All the students stop and look at me and innocently ask me what cock is, as I have repeatedly told them its not a word unless you can use it in a sentence.  I quickly say its a male rooster and change the subject.