Slugs live in dark, damp places during the day and come out at night to feed. This one has come out from a hole in a nasty place. It’s quite funny really, there is a mass exodus from its home each night with it and many of its fellow slugs all taking shelter there during the day and all going off to do their sluggy slimy business during the night. It creeps over the wall that houses it in a search of food. Being out in the dry causes them to desiccate, but not in a good, coconut-ty way, hence the need for quiet repose.