[Caryatis]

possibly from this?

line 849 from mob.cpp

	// hp event 
	if ( IsNPC() && ( GetNextHPEvent() > 0 ) ) { 
		if ( ds->hp < GetNextHPEvent() ) { 
			int lasthpevent = nexthpevent;
			parse->Event(EVENT_HP, GetNPCTypeID(), 0, CastToNPC(), NULL);
			if ( lasthpevent == nexthpevent ) {
				SetNextHPEvent(-1);
			}
		} 
	}