“ An heir cannot lay hands [on the head of a sacrifice] nor can an heir effect exchange [with his father's dedication] . What is R. Judah's reason? — We infer the case of a preliminary act in the dedication14 from the case of a final act in the dedication.15 Just as in the case of the final act, an heir cannot lay hands [on the head of a sacrifice] , so in the case of the preliminary act, an heir cannot effect exchange [with his father's dedication] . ”