"You lookin' at me?"

"If it looks like a duck, and quacks like a duck, we have at least to consider the possibility that we have a small aquatic bird of the family anatidae on our hands."

"If it walks like a duck, quacks like a duck, looks like a duck, it must be a duck"

"Be like a duck. Calm on the surface, but always paddling like the dickens underneath."

Abroad, flat bill, short legs, and depressed body = DUCK!