Analysis of information sources in references of the Wikipedia article "Luz (bone)" in English language version.
I have been to distant lands, and heard there that this is the name of the bone of the spine. Of all the bones this one remains in the grave. It is called 'Betu'el the deceitful'. I asked about it, and they said that its shape resembles a head of a serpent, which is deceitful. And that more than any other bone in the body, this bone is deceitful.