That reminds me of many years ago when we just used to leave the kitchen window open for the cats to get in and out at night. We used to call it the "aerial catflap". Certainly wouldn't do that nowadays (in fact probably shouldn't have done it then, as London in the mid eighties wasn't exactly crime free. Actually somebody did try to burgle the upstairs flat but got more than they expected, there were half a dozen large Australian blokes there at the time who sent them packing).