Recently I read Catwatching by the veteran zoologist Desmond Morris. In addition to details of feline behaviour, he discusses how various cat-related terms came about. For example, we are all familiar with the expression no room to swing a cat. This refers not to the animal but to the cat-o'-nine-tails, a flogging implement used on board old sailing ships. Miscreant mariners had to be flogged on the open upper decks, since there was no room to wield the punishment device in any cabin. The whip itself was called a cat-o'-nine-tails because it left scars on the sailors' backs that resembled the scratches of a real cat.
We are all also familiar with the saying to rain cats and dogs. Many centuries ago, towns and cities had narrow filthy streets and poor drainage. Torrential rains would cause flash floods, and large numbers of stray cats and dogs, that had scraped a living in the mean streets, would perish. After the downpour, the corpses of these animals would be revealed and it would seem to the superstitious that they had indeed fallen from the sky.
To let the cat out of the bag is another common phrase and refers to an old market trick. Piglets to be sold were taken to market in a small bag, often called a poke – hence also the expression a pig in a poke. Unscrupulous vendors might put a cat into the bag and pretend it was a pig. If the buyer insisted on seeing it, he would be told that the animal was too lively to risk opening the bag as it might escape. If the cat did in fact succeed in fighting its way out of the bag, the secret was revealed – the cat was out of the bag.
To not have a cat in hell's chance seems somewhat inexplicable, until one learns that the original, longer phrase was 'no more chance than a cat in hell without claws', meaning that a difficult situation is hopeless unless one is adequately armed.
The expression to have kittens, meaning to be frantic, upset or in a complete state of turmoil, dates back to medieval times when cats were suspected of being the familiars of witches. Any pains that a pregnant woman suffered were believed to be a result of her being bewitched, and that she had kittens clawing inside her womb. Witches were believed to be in control of cats, and could concoct magic potions to destroy the litter so that the pregnant woman would not give birth to kittens. In those superstitious times, an excuse for procuring an abortion was given in court as 'removing cats in the belly'.
Finally, why does a cat have nine lives? This is because nine was considered a particularly lucky number, as it was a 'trinity of trinities' and thus appropriate to 'lucky' cats.