Fast acceleration period. Likely from standstill to have max torque. Plus a large offset between the casket's original position and the window. Then if there is something sharp on the top of the casket that will help it crack and make it that much easier. Really though, even with the cracking it would probably crack as a result of the casket coming to a sudden and complete stop. Getting it out of the car requires acceleration after that point, which is also possible. So hard acceleration, sliding, bang, sound of shattering glass, hits the gas harder when startled, flies out. Source: I have experience with a tv flying through the window of a van.