The face on Stone 5 is important because it is unequivocally a carving!   There are those who claim that the Avebury stones are all raw sarsen, with no human artistic input. They claim that any resemblances to faces or animals or symbols in any Avebury stone are merely natural accidents.   Stone 5 proves they are wrong.  The appearance of the face here is wholly unnatural. You can see the sculptor's work in the ridged shadow area on the right of the nose, and in the gruesomely clear left eye socket - these were deliberately hacked out by hand with considerable skill.

Stone 5 puts it absolutely beyond dispute that there are carved faces at Avebury.

Furthermore below the nose there is a shocking sea of rough stone, utterly unlike the smooth surface of the monolith as a whole.   My first thought was whether there had been a mouth here that was later smashed away, leaving a terrible scar?

However my son Josh has a better suggestion.   His view is that the rough area is not prehistoric vandalism, but part of the original sculptors' design.   This makes me wonder therefore if the statue represents a shocking image of a corpse in the process of disintegration , where the rough/hacked area represents ripped and half destroyed lips.

This is not as outlandish as it sounds, neolithic people practiced excarnation, the deliberate exposure of their dead in the open air, the bodies being stripped of flesh by birds and animals.  My limited understanding is that birds in particular might eat a corpse's eyes first, then I assume the lips might be high on the list of body parts to take next?  

On this basis our statue represents human mortality and brutal decay, but with the mitigating hope that the propitiations of Avebury ceremony with enable this individual to be reborn at the pleasure of the Great Goddess.   The endless cycle of death/rebirth celebrated in stone.