Personality quirk, I'd say, but who knows? My Devon Rex spay girl has a thing about shoe laces too....so I know what you mean about all "slimy"! Problem is she bites them off and swallows them, and occasionally they come out in her poop, or even after 2 wks, she's barfed it up! We've had to resort to putting in a stick in our sliding front closet door, and trying to keep the shoes up on a rack off the floor. My fear is an intestinal blockage, which would result in surgery and a big vet bill $$$$. Fortunately our girl doesn't like Bitter Apple, but I'd really get a shoe rack that she can't get at the shoes....maybe one of those plastic enclosed zippered hanging shelf ones might do the trick.