The airplane's engine battery was dead so the pilot elected to hand-prop the engine. He tied the tail of the airplane down via a brass snap-hook that attached to a metal fastener underneath the airplane's tail section. The snap-hook was attached to a rope that was secured to the ground. The pilot set the parking brake and checked the throttle position; however, he did not secure the wheels with chocks. The engine started on the third attempt and RPM increased as the pilot walked back toward the cockpit. Before he got there, the brass snap-hook broke and the airplane began to roll forward. The pilot was unable to access the cockpit and the airplane traveled unattended until it collided with a parked airplane resulting in substantial damage to the right wing.