We just retrieved Heidegger, our exceedingly intelligent cat from under the couch in our across-the-alley neighbour's house.

It seems he followed one of their cats in through the cat-flap, got inside, and immediately got lost. He spent most of the day inside their house (at least 8 hours), and was totally petrified when I found him.

So thanks to Paul, our across-the-alley neighbour for hearing his tags jingle when he came home from work, and seeing him dart into their living room, then suggesting that he might be under the couch (since that's where his other cats hid when they first got there).

Bratty cat.