Our large male cat, Soot, had become too large, and so we’ve recently put him on a diet using a cat-food dispenser. At about the same time, despite the fact that he’s long since been neutered, he began to regularly attempt to have sex with our other cat, a small spayed female named Smoke. Both are about 14, and although he’s done this in past occasionally, he’s now trying to hump Smoke on a daily basis. For her part, she doesn’t seem to mind it much; he’s the one that makes all the noise, leaving her with only a moist bite mark on her back after we break them up. Any ideas as to why he’s suddenly turned so amorous?