God said the woman's offspring would crush the serpent's head, and the serpent would strike his what?

Answer: Heel

"He will crush your head, and you will strike his heel" (KJV: "bruise his heel").

“And I will put enmity between you and the woman, and between your seed and her seed. He will crush your head, and you will strike his heel.””— Genesis 3:15 (BSB)