Dysphoric Rituals of the Paleolithic

Why do so many prehistoric cave paintings have spray-painted outlines of hands with missing fingers?

Mundane social science interpretation: "The pain and mutilation create cognitive dissonance which justifies close social bonds"

Better: "SHAMAN FINGER BONE MAGIC APPEALS FOR SUPERNATURAL ASSISTANCE"

Shaman class ability, can amputate a finger given 1 round and a suitable tool.
Drawbacks: Take 1 hp damage per character level, and permanent -1 DEX per lost finger, cumulative, when using that hand (-3 for second finger etc.)
Benefits: Access to one spell as if 5 character levels higher, can cast it even if expended for the day. Must strip and eat the flesh from the bone to cast the spell.

Fingertip option: remove a fingertip for half the DEX penalty (rounded up) and access to a bonus spell at existing caster level.