
The worst thing one of my cats did some years ago was to get into the house via the kitchen window.
It was Christmas and I had a warm dry conservatory and a cat flap in the door, so when I went away for Christmas for four days I imagined my cat snuggled up in the conservatory and a kindly neighbour to feed him.
What I did not know was that a pane of glass in my kitchen window was broken and so although the neighbour was thinking all was well and the cat was certainly eating in the conservatory and snuggled up on the sofa there, the full horror of his antics was not discovered until I got back. A friend of mine who was coming to stay had a key from me, and on entering rang me to say I'd better get home quick!
On arrival home the little monster had obviously found a rat colony somewhere, there were bits of rat and whole rats all over my kitchen, dinning room and hallway! yuck and big grump!