She made him sleep on her knees; and she called for a man, and shaved off the seven locks of his head; and she began to afflict him, and his strength went from him.
The fact that Samson told Delilah to do something to his hair (Judges 16:13) suggests that he was giving her a clue to his strength. She did not pick this up but kept hounding him for his secret. Finally he gave in (Judges 16:17; cf. Judges 14:17).