McMahan argues that Caller is not liable to be killed because, unlike Driver, Caller has no reason at all to suspect that using his activity will endanger an innocent person. Since Caller does not knowingly risk harming Victim he is not morally responsible for posing a threat. But, despite McMahan’s suggestion that there is a difference in kind between cases like Driver and Caller, it seems more like a difference in degree (McMahan 2005a: 397). It is, clearly, not impossible that the phone is rigged. The difference is rather that, on Caller’s evidence, the chances of its being rigged are tiny, whereas Driver’s evidence suggests that she has a somewhat greater (but still very small) chance of harming an innocent person. McMahan’s account of moral responsibility thus depends on the idea that small differences in foreseeability are very morally significant. Driver is liable to be killed to save Victim; Caller is not.