Member
A shellfish with a mouth is a member of the invertebrate family. Yes, shellfish do have mouths, look it up!
Imagine a shellfish opening and closing its mouth, talking to you and telling you what a proud member of its family it is. It’s a strange sight, but picture it in your mind anyway.
いん
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If you were a member of the same shellfish family, you'd be able to go to the special shellfish inn (いん). Every species has a members-only inn.
Imagine trying to go to the shellfish inn. Imagine all the members-only signs telling you that you can't come in. Womp womp.