Final answer:
When the stone sank in the Philistine's forehead, he fell to the ground.
Step-by-step explanation:
According to the Bible (1 Samuel 17:49), when the stone sank into the Philistine's forehead, he fell to the ground. This incident is part of the story of David and Goliath, where David, a young Israelite shepherd, defeated the giant Philistine warrior Goliath with a single stone from his sling.