Our two cats seem to get joy from the oddest things (besides the usual tin of cat food being opened of course!)
BoyCat loves nothing better than to shred a roll of toilet paper. We've stopped hanging it on the actual holder in the bathroom now, otherwise he'll happily pull it from the roll, shredding it into a million tiny pieces as he goes. (He knows he's not allowed to as you can see by the guilty look on his face in the picture...
)
GirlCat has a weird obsession with cotton buds. If she sees one, she'll meow at it until she can get hold of it and chew it. I've had to move where I keep them as she worked out how to open the drawer with her claws and get into the box.
What random things or objects do your cats get weirdly excited about? 