A watch dog !
A Labracadabrador.
A "shhh"nauzer
Nothing, she's already been told twice.
3, duh. (My ex's 9 year old little sister told me this joke, and followed is up with: "and YOU'RE the math guy!" >< Burned.)
It'd be a waste of time.
if you lay them right the first time, you can walk all over them for years.