Stray Snail

So I was cleaning the other day and found this fellow - he is dead, unfortunately - on the windowsill under the window in the livingroom that we open to air the flat.

The fellow is very small, only about 4 mm long, and I wonder about his natural habitat, because the window he must have come through is on the third floor. I know they are good climbers, we saw many of his cousins when we were in Österlen (southern Sweden) a few years back. It has been very windy, though - perhaps he flew in?