POLL: Why is it considered necessary to nail down the lid of a coffin?

so the zombies don't come and attack people, duh.POLL: Why is it considered necessary to nail down the lid of a coffin?
So the body doesn't fall out if the pall bearers slip.POLL: Why is it considered necessary to nail down the lid of a coffin?
its probably an ancient superstition that no one can quite really remember
so its harder to steal a body???