How did the woman identify Huck as a boy (what gave him away?)

Mrs. Loftus throws a piece of lead at a rat in order to judge Huck's aim, as she is suspicious of his gender. Afterwards, she reveals where Huck went wrong with his "girl" behavior and asks him what his real name is, telling him to be honest. Huck cleverly pretends to be an escaped apprentice hiding in women's clothes to avoid detection.