All I can figure is that Floppy either lost his collar on his own, as he does frequently, or another cat knocked it off when they were rolling the old man, and Ambercat started playing with the collar, and somehow "nosed" it perfectly and it ended up around his neck. Floppy's neck is quite a bit thicker than his, as can be seen on the collar.
I'm at a loss as to how he pulled this one off. I was looking everywhere for Floppy's lost collar, and then I found it yesterday. He was wearing it over his collar......