You can bite the inside of your mouth in such a manner that it makes you more likely to bite the same spot again.

Your body is constantly afraid that it's going to starve to death at any moment, to the extent that it stockpiles fat to such a degree that you can die of too much fat stockpile. If you start getting exercise and burn some fat, your body will adjust to try and stockpile fat even harder, so you have to increase your exercise load to keep ahead of the system.

Pain has a emotional component. It's not enough that we are aware of damage being done to our body, but rather sometimes that awareness is so strong that it renders us incapable of defending or repairing ourselves. Meanwhile, any number of other animals can full-on get a major limb ripped right off and they just keep on keeping on like it's no big deal.

Also, vertebrate eyes (left below) have a blind spot because the nerve wiring is routed in front of the retina and needs a path to get out of the eyeball, so there's a spot with no photoreceptor cells where all the fibers run out.

It doesn't have to be this way - cephalopod eyes (right) have the nerves running out the back of the retina so they don't need a pass-through hole.

A number of rodents have a similar problem. Squirrels, as well as others, have their teeth that never stop growing. This is why they need to chew on twigs, nut shells, etc to wear down the ever growing teeth.