Proverbs 25 says feeding a hungry enemy will heap what on his head?

Answer: Burning coals

If your enemy is hungry, give him food; "you will heap burning coals on his head, and the LORD will reward you."

“If your enemy is hungry, give him food to eat, and if he is thirsty, give him water to drink. For in so doing, you will heap burning coals on his head, and the LORD will reward you.”— Proverbs 25:21-22 (BSB)