Terry Pratchett is particularly fond of knees.
More than once, he has used an expression describing an abundance of knees, or an excess of knees, or suddenly growign extra knees, to describe his characters.
While the concept is, visually, one I can understand, I feel like I am not quite getting the exact meaning of this 'knee-abundance' he writes about so often. Particularly in Mort, where the main character has an abundance of knees, and in Jingo, where a camel grows 'extra knees' as it speeds up. The former being used to describe an unfortunate trait that I don't quite get, and the latter simply describing the camel's sudden increase in speed.
Is this a regular expression in British English, where a person grows or has an abundance of knees? Or is Pratchett just making up an expression that manages to fly over my head?