English: “His hand on the head” — and not the back of his hand (so that there be no interposition between his hand and the offering).
In Sifra: Contact must be direct. Even the back of the hand is treated as a failed form; and by the same logic, any object between flesh and animal is chatzitzah. “His hand on the head” means palm-to-head continuity.
Type of Learning
Diyuk against chatzitzah — no interposition between hand and head.
What Is Learned
Nothing may interpose between the owner’s hand and the animal’s head during semicha. The contact is direct; a barrier, or leaning with the back of the hand, fails the form of “his hand on the head.”