Something funny - even not polite - happened when I put on a wall of my University (Department of Mathematics) the AWAD-quotation

Arithmetic is being able to count up to twenty without taking off your shoes.
Mickey Mouse

An anonimous student added the following

...or to twenty-one without taking off your slip.
Minnie

(In Italy Mickey Mouse is "Topolino" (= small mouse) and Minnie his girl friend)