Not sure about the 'dead' bit, but references to 'no room to swing a cat' dates back to the cramped conditions of the sailing ships, when discipline was administered by flogging with the 'cat' - a cat o' nine tails whip. a fearsome instrument with nine separate lashes bonded to one handle which could inflict severe injury, and was a feared form of punishment. Obviously, enough room was required to 'swing the cat' in order to administer the punishment, and that was done on deck because below deck there was 'no room to swing a cat'. Often, the 'cat' was left in a canvas bag, tied to the ship's mast, to remind people of its presence, and this gave rise to the phrase 'letting the cat out of the bag' implying that someone had caused enough trouble to merit a flogging.