A scale.
or
Because there's no one else to wag it for him.
or
100: One to do it and ninety-nine to say "I could've done that."
or
Hot, because you can catch cold.
or
Drinking, bathing, washing, swimming, etc.
or
Bike helmets don't fit hippos
or
None, because they were copycats
or
Big holes all over Australia!
or