Our downstairs neighbour has a lovely little kitten, but no cat flap in their back door so he sits outside mewing most evenings.
We have a cat flap but no cat. The cat has worked out that if he doesn't get let in by his own humans at night, he can get into our flat through the flap as the lock doesn't work. All fine and dandy for the last few weeks, we have a friendly little cat visitor every now and then.
Backfired yesterday: he brought us a dead bird. Feathers everywhere. Cat was very quick to leave (with the bird, thankfully).