get a clue

Hey diddle diddle
The cat and the fiddle
The cow jumped over the moon.
You've read Fox in Sox
Now go find a box 
That you know can carry a tune.

They say you can't tell 
a book by it's cover;
I'm not really sure if that's true.
  
To whatever extent 
The jokers came and then went,
Beware:

On Monday they're coming for you.