Fat, it's fat.
It's an extra flap of skin on an animal and on rabbits it's fatty. Generally female rabbits have nice fluffy ones for nest building.
It isn't neck poof or fluff but it's ok if you call it that... but still, it's a dewlap. A fatty fat roll of fat on my fat neck :D.
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JoyBunny
Deeeeewlap <3 I'm so glad to see a bunny character with one for once <3 I was designing an English Lop with one, but never finished...