Why shut and nail down the lid of a coffin?

So, why would anyone do that? If we get out the old history books we would  find out that egyptians and old cultures used to bury their dead with jewerly and belongings, so maybe nailing down the coffin was necesarry to prevent robberys and such. But nowadays, you pretty much bury the old man/woman with whatever old clothes he/she had, some earrings (if she is a woman, or a kind of liberal man) and that is pretty much it, so what is the point?

The possibilities are actually funny, maybe people are scared of them waking up, so they make sure to seal it shut to avoid that option… just in case the person decides he isn’t dead and starts knocking down doors. The other possibility is that of a rise of the dead kind of mood, I mean hey, we have enough living people that can become zombies, why would we want dead people to become zombies also, better keep them nailed shut in their coffins. Another “intelligent” reason could be to prevent rats and other crawler from gaining quick and easy access to the coffin… if they want food they have to get it the hard way, bite their way in or something!

So what can we take of this?... there really is no logic behind it… so.. we should maybe, stop doing it?