This is all I know about it at the moment so I can only speculate as to the story. I am going to assume that the sarcophagus holds the body of an ancient bird who possibly comes back to life (like the Mummy stories from Egypt). I know some of my readers might say I’m jumping to conclusions and no birds are involved, but you must remember that this dog knows that birds are evil so it is a logical assumption. Maybe it is the mummy of a bird that goes amok and starts killing the humans.
This leads me to another observation. Divers go underwater, and all us dogs know that baths involve water, and this dog, like so many others, is not fond of baths. Perhaps the humans should re-think the whole idea of getting into water so much. If those divers had stayed on land, there wouldn’t be an ancient evil loose in the movie.
Of course, I might not be correct because Vault was probably written by a human. However, if Vault had been written by a dog, you can be sure that the “evil” would involve a bird or maybe a squirrel!
Demon Flash Bandit (My Thoughts on Vault)