The causal account captures the intuitive permissibility of using defensive force against Falling Person in Ray Gun. It also permits killing morally responsible (but non-culpable) threateners such as Driver. But this broader scope of defensive permissions is secured, at least on Thomson’s construction, by endorsing the controversial view that one need not exercise agency in order to violate a right. Merely causing Victim’s death, when one lacks a right to do so, suffices. It also holds that one can be under a duty to refrain from doing something even if one is unable to refrain. Several commentators argue that Thomson’s view entails, implausibly, that falling stones can violate rights (McMahan 1994: 276, 2005a: 388; Otsuka 1994: 80; Zohar 1993: 608; Rodin 2002: 85–87). Stones lack rights to kill. Thus (it seems) Thomson must think stones under a duty not to kill. If so, they too must fail in this duty, and therefore violate rights, when they kill.