My precious Tuppy brought me a couple of "reds" (for which read red bellied black snakes!) when we lived in Sydney. They were - of course - alive and wriggling, only smallish (about two to three feet), but where there are little snakes there are big momma and poppa snakes! She used to pop in the cat door and drop them on the kitchen floor and cry out for me to come see. Generous little girl!
Big old Maroo would often bring prey home, but only for me to admire. He wasn't gonna hand them over to anyone. He would sit on the front door mat to feast (I went through a lot of door mats in Sydney!! lol), and one day I actually saw him take one big crunch and a tiny head fell out one side of his mouth and the tail out the other side. He then sat there watching me and literally crunched his way through a field mouse. Revolting beast! He could be sweet sometimes, but that brought home to me that a cat is a cat, and a cat can revert to wild animal behaviour whenever and wherever!
'Roo also brought me a mouse one night and dropped it on the bed. Now, for those not familiar, summer in Sydney is HOT, so I had only a sheet on the bed. Mouse moved, cat (all
20lbs of him!) pounced, I screamed in agony as half a dozen pitchfork-sized claws pierced me. The cat-and-mouse game continued for some time around the house as I administered first aid to my cuts and staunched to considerable blood flow.
Another time he dropped a dead mouse on the floor right next to the bed. In the morning I got up very early for a 5am start and it was still dark. You haven't experienced true horror until you feel that squishy feeling between your toes, realise what it is you stood on, and then have to hop all the way to the bathroom to avoid leaving bloody footprints on the carpet!
My neighbour's cat - Henry Z - brought home a six foot tiger snake (if you aren't from OZ, this is not the sort of thing you want anywhere near you!) and dropped it right behind her on the kitchen floor. It was alive, and A just screamed for DH and jumped up on the kitchen sink. DH arrived and screamed and jumped up beside her! (Should explain, they were from UK and never adjusted to having these sort of things all around when they lived in the Blue Mtns, NSW) Henry continued to play with his new toy on the floor. Finally they managed to call through the window to a neighbour to come deal with the unwelcome intruder.
A made DH nail the cat door shut after that, and Henry was confined to the laundry at night!
I think anyone with a cat/dog door could tell a story or two about unwelcome "visitors". But not having a pet door doesn't guarantee that the UVs won't get in anyway. I had a friend find a full grown possum in her kitchen one night, calmly devouring a pack of choc biscuits. The possum had got in through the exhaust fan over the stove.