Teratoma (from greek terato and oma, meaning monster tumor) are tumors that can be found in areas of the lower end of the spine and contain multiple types of cells and can form things such as bone, hair and teeth.
Some are more cystic while others can be more solid.

These ones are cast in resin from original sculpts and can just hang out or be on a necklace. Because they are grab bad, you will receive whichever one I happen to pick up first.