a grey fluid-sack

This was undoubtedly once a part of some creature. It is not large, and inside you can clearly see some dark fluid.

It is a grey fluid-sack.
It weighs half a pound.

You identify a grey fluid-sack.
It weighs seven ounces, and it is worth about five lauren and five celeb.
Its keywords are sack, fluid-filled, grey, fluid-sack, and greyfluid-sack.