I have one rat who isn't blind. So obviously nothing makes me happier than watching it roll itself around the house smashing into walls searching for god knows what. Because of rats exceptionally long tails they needed the 11.5 inch diameter one. Kind of ridiculous that the 6.5" one is $9.99 but the 11.5" one is $24.99. My brain doesn't do math but something seems wrong there. You may find that if your rat or large animal has particularly poor eyesight or a temptation to scale walls, that upon smashing the door bits of ball against walls enough the locking grooves may start to crack and thus break after time.