doesn't only happen to humans....
Years ago my uncle had a rather lovely dog (a retriever, I think). Anyway, he used to take the dog everywhere, including in his motorcyle sidecar, for long walks in fields and so on. One day the poor thing started to struggle to use its back legs - it was getting old and the first thought was arthritis, or some other similar old-age related problem. After a couple of days the dog was showing signs of pain and extreme difficulty in walking so it was off to the vets.

The vet quickly ruled out arthritis as there was good movement in the joints and so proceeded to check other areas of the poor suffering animal. Turned out that the dog had severe grazing and bruising on both nads - at that point everybody remembered how the dog had struggled to jump over a fence whilst walking just a few days earlier and must have smushed his poor dognuts against the woodwork! unlucky!
(downhill without brakes . It was the worst day of my life, Sun 16 Jul 2006, 16:01, Reply)