Q: What happened to the mouse when he fell into the bathtub?
A: He came out squeaky clean!

Explanation: Just as a cow says “moo” and a pig says “oink,” mice squeak.  If you are interested in hearing an hour of mice squeaking you can listen here (although I am not sure why you would want to).

Squeaky clean is an informal phrase meaning that something is really, really clean.  A window that you just washed could be called squeaky clean.  Squeaky clean can also refer to a person’s character–the senator was squeaky clean: he never lied, misled or cheated anyone.

This joke is funny because it plays with the word squeaky, meaning the sound of a mouse and completely clean.

Here is Tom and Jerry getting things squeaky clean–