A mouse is a cat that is kept for the purpose of catching mice. In England, there has been a mouse at the Prime Minister's residence for centuries. The most popular of these cats was a stray named Humphrey who, in 1989, was the first cat to receive the offical title"Chief Mouse to the Cabinet Office."His care cost 100 pounds and was paid from the department's budget. It was said to be far cheaper than the fees previously paid to exterminate. Humphrey, who was beloved in the UK, retired in 1997. The current mouse, named Sybil, took office in September of 2007