A mouse can squeeze through a tiny hole

If you think closing your front door keeps the vermin out, science has some terrible news for you. A mouse's skull and collarbones are incredibly tiny, and their rib cages are connected by flexible cartilage. This allows them to flatten their entire bodies like a furry pancake. If their head can fit through a hole about a quarter of an inch wide, the rest of their creepy little skeleton is following right behind it.