وَالِانْكِسَارِ فِي الزُّجَاجِ عَقِبَ كَسْرِ إِنْسَانٍ
The breaking that occurs in glass following a human act of striking it.
Pain and fracture are useful examples because their effects occur in a subject other than the agent’s own body. A person intends the movement of their hand, but another person’s sensation or the change in the glass is a distinct occurrence, not simply the same voluntary movement.
This introduces the question of the locus of human capacity: which actions and which subjects fall under the servant’s acquired power? That question underlies the disagreement over creation and acquisition.