Look here for an explanation.
Of course, we mustn't forget...
"Who brings the cheese on April 3rd?
The Cheese Weasel
He's not a silly bunny or a raindeer or a bird,
He's the Cheese Weasel
He's got a cute black tail
And tiny buck teeth
He doesn't bring fish, and he
Doesn't bring beef
So you'd better be good if you wanna get some cheese
From the Cheese Weasel."