Holbrook (D) owned a walled garden about a mile from his house. D had problems with people stealing things from his garden. In an effort not to prevent intrusion onto the property but to catch an intruder, D set up a spring-gun trap in this garden. He did not post notice of this trap. Bird (P) innocently chased an escaped bird into the garden. P climbed the back wall and called out his presence. He received no reply and proceeded. He set the trap off and severely damaged his knee. P sued for the damage cause to his knee by the spring gun trap. D claimed that P had no action because he committed an act of unlawful trespass.