I read on some site that a teacher used them in the first day of the class to break the ice.

He gave an example of how he would do that. Here is the joke:

There is a family of mice having dinner when suddenly a cat jumps up to the attic and snares her teeth.

The father mouse jumps off his chair and say "Wuff wuff".

The cat, scared, runs away. The young mixe, in amazement over what just happened, ask their father, "What was that, Dad?"

The father mouse replies, sipping his milk, "That my children is one of the benefits of learning a second language"