What is 1 plus 1?

A psychopath escaped from a mental hospital and got a gun somewhere. At midnight, no one went to Hong Kong. He lurks in a dark corner. At last he waited for someone, a young man. He jumped out, pushed the man to the ground, pointed a gun at his head and asked, "What is 1 plus 1?" . The man looked uncertain, hesitated and said, "2?" Mental patients pull their fingers at once. Bang! The man fell down. The unspeakable loneliness on the mental patient's face said to himself, "Hey ~! Don't blame me, you know too much. " Is this it?