* "Foul" has two meanings:
* Unfair or illegal: This is the intended meaning in the context of stealing, making it a "bad" or "wrong" action.
* Related to birds: This is a secondary meaning, specifically referring to a bird, like a duck, belonging to the order Anseriformes.
By using "foul" in this sentence, it plays on both meanings. It creates a humorous effect by suggesting that stealing ducks is not only a bad deed but also somehow related to the birds themselves.