Single indoor cats are very prone to boredom and depression. They eat because the food is available and there's really nothing else to do. Combine that with the general lack of exercise and it's not hard for the cat to become obese.
It was a major factor in my choosing to adopt a pair this time around. They keep each other pretty busy. They play this game and have since they got here: one stalks, pounces and chases. The other runs. They take turns and seem to switch being "it" every day or so.
It's funny to see Kaylee when it's her turn to pounce. Zoe's almost twice her size and weight, but Kaylee's surprise tackles are right out of Aussie-rules. I've seen Zoe get utterly flattened more than once.
