Their little lives are so proscribed; trapped in a cage, even my 135 gallon terrarium is confining if that's where they are the majority of the time. If they are happy with an extra mouse, fine by me. If I'm anthropomorphically thinking they are happier with an extra mouse, thats OK also. If it means they have high cholesterol levels, atherosclerosis, and snake diabetes, (if a snake can even get diabetes secondary to obesity) they may indeed live a shorter span, but perhaps, more contentedly. And that is fine by me as well.