An idiomatic phrase expressing that if something looks and acts a certain recognizable way, it probably is exactly what it appears to be.
"After the liquor store was robbed, a man was found leaving the scene carrying a gun. Did he commit the crime?"
"If it walks like a duck, looks like a duck, and quacks like a duck, it's a duck."
"If it walks like a duck, looks like a duck, and quacks like a duck, it's a duck."
by AH73 October 18, 2013