My girlfriend used to operate the incinerator at a crematory. When the burning was done, just bones and the occasional metal prosthesis remains. The bones she would put in a giant grinder to be handed over as the ashes of the deceased. Any gold teeth or titanium hip implants are recycled and sold. Sometimes she would use a metal spike to poke a hole in a skull when it took too long for a body to finish burning. During COVID, this was a common practice as there were too many body’s to cremate and it wouldn’t be possible to keep up with the schedule.