On Dartmoor we have large slugs. I mean really, really big ones. I hadn't realised this until I really started looking, but slugs have a breathing hole on the side of their neck. I believe it's always on the right side, although the distance along the body can vary. The hole is called a pneumostome. (I pronounce it so that it rhymes with "home".)
Your prompt for this month: find a small hole, perhaps even a slug's pneumostome.