It's always an estimation of course. But if you are going to damage a bone sufficiently to leave a deep mark with a (probably sharpened rock) spear then it real

It's always an estimation of course. But if you are going to damage a bone sufficiently to leave a deep mark with a (probably sharpened rock) spear then it really helps to have a hard surface underneath to do so. It could have been standing and then pushed up against a wall but two hands thrusting it downward is safer bet.