Looks more like the end of a piece of wood than skin. It may be a piece of your substrate which has punctured the skin in that area and is acting like a large splinter. Try gently pulling on it with tweezers and see what happens.So Munch has a piece of skin in his neck/shoulder area that is like a little rectangular bit that kinda hangs off, but isn't fully off. Is this something to worry about? I've noticed he has had increasing amounts of peeling/shedding little bits like this.
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