The ship's cat has been a common sight on many trading, exploration, and naval ships, and is a phenomenon that goes back to ancient times. Cats have been carried on ships for a number of reasons, the most important being to catch mice and rats. These rodents, when aboard, could cause considerable damage to ropes and woodwork. More serious was the threat rodents posed to the stores the ship carried. Not only could they devour the foodstuff carried to feed the crew, they could cause economic damage if the ship was carrying grain or similar substances as part of its cargo. Rats and mice were also sources of disease, an important consideration for ships which could be at sea for long periods of time. Cats naturally attack and kill these rodents.