Do you think perhaps Mr P has......
Luxating patella (or trick knee, subluxation of patella, floating patella, or floating kneecap? 
Taking of flatulence (weren't we?) I have a problem with one of mine. Dogs, that is. He just seems to be carrying a mild miasma of iffy smells around him. This is very recent, no dietary changes and no, how can I put it, obvious eruptions. He's been bathed, wiped down daily, even sprayed with perfume, but this vague odour hangs about him. I've googled obvious things like anal glands but he has no symptoms. I suppose it's a vet visit unless anyone can suggest a cure?