Unfair but sadly necessary. Arnie & Mullie (named by my wife, believe it or not - I wasn't really a fan of calling cats such strange names as Arnage & Mulsanne, and whenever we take them to the vets/cattery etc, people always ask what their names mean... and you explain they're corners on the Le Mans 24 hour circuit, and a look of quiet sadness glazes over the eyes of the person asking ... "Oh, really? that's interesting...") are brother and sister, and his developing libido was showing too much interest in his sibling for comfort.
I wouldn't want to deal with a litter of three-legged, 4-eyed kittens that might result