I saw this and a bizarre, rather macabre idea sprung to mind. A bag of holding is a great low level magic item that every adventuring party loves to have. The best way to get a magic item is to defeat a bad guy, right?
So there's a crazy wizard that's been studying a variation on animating dead bodies, with the specific aim of raising a swarm of dead cats. He has made this the subject of his master's thesis, much to the horror of the academy where he would present his findings.
He left the academy to pursue his research independently, and begun collecting the bodies of cats he abducts in the middle of the night. He stores them in a bag of holding he stole from the academy. The players get the bag of holding if they defeat him, but inside...
Just an idea for a low-mid level minivillain.
I suspect, somehow, at some point during the adventure, that bag is getting swung.