When a person loses a leg, we concentrate on replacing that leg with a prosthetic so they can walk in the normal way humans walk. But quadrupeds like dogs and cats can lose a leg and get around pretty well on the three that are left. But not perfectly.
YouTube engineer Simone Giertz has a three-legged dog named Scraps. As she ages, Scraps showed the effects of wear on her remaining hind leg, since it had to carry the weight that two normal legs should. Adding a prosthetic leg to a dog who was already used to three legs would be difficult, if not impossible, so she concentrated on relieving the burden of the remaining leg. Giertz decided on an electronic leg brace, or an exoskeleton, on the one leg to give her a power boost. Giertz did her research, which involved buying stuffed animals, and training, which involved Scraps. Then she wired the whole thing up in a manner that was acceptable to Scraps, which involves some NSFW language. A good time was had by all. There's a one-minute ad at about 4:30. -via Laughing Squid