(to rhyme with “now”). You have got the wrong sow by the ear. Sow is a large tub with two ears or handles; it is used for pickling or sowsing. The expression means, therefore, You have got hold of the wrong vessel, or, as the Latin phrase has it, “Pro amphorâ urceus” (You have brought me the little jug instead of the great gotch). French, seau (a bucket).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894