pf2e.fyi
From Pathfinder Adventure: Prey for Death, which isn't enabled.

Erupting Spurs

REACTION
Activity reaction

Trigger A creature takes persistent bleed damage from your bone flense spell

Effect You will the bone spurs to erupt in a particularly devastating manner, dealing 6d6 piercing damage (basic Fortitude save) to the triggering creature instead of the persistent bleed damage from bone flense. The duration of bone flense immediately ends.
Pathfinder Adventure: Prey for DeathORC