flagellation_decision_effect

flagellation_decision_effect = {
	#Get both rewards
	if = {
		limit = {
			has_trait = flagellant
			has_personal_tenet_flag = self_mutilation_active
		}
		stress_and_fulfillment_impact = {
			flagellant = major_stress_loss
		}
		add_piety = medium_piety_value
	}
	#Only Piety
	else_if = {
		limit = {
			has_personal_tenet_flag = self_mutilation_active
		}
		add_piety = medium_piety_value
	}
	#Only Stress-loss
	else_if = {
		limit = { has_trait = flagellant }
		stress_and_fulfillment_impact = {
			flagellant = major_stress_loss
		}
	}
	else = { add_stress = major_stress_loss }

	#Be kind to the AI
	if = {
		limit = { is_ai = yes }
		random_list = {
			75 = {
				#No increase
			}
			25 = {
				increase_wounds_effect = { REASON = whipping }
			}
		}
	}
	else = {
		increase_wounds_effect = { REASON = whipping }
	}

	#Not already flagellant?
	if = {
		limit = {
			NOT = { has_trait = flagellant }
		}
		random = {
			chance = 20
			add_trait = flagellant
			add_stress = major_stress_loss
		}
	}

}

As written in game/common/scripted_effects/00_decisions_effects.txt.