Henry Shue's critique of torture is decidedly non-utilitarian. This means that he doesn't reject torture because of its harmful consequences, but because it is intrinsically wrong. According to his argument, torture can, under certain circumstances, be worse than killing someone. Whereas torture always involves inflicting suffering on a defenseless person, killing can be justified in some cases, such as when a soldier kills an enemy in battle. The soldier who dies in combat is usually not defenseless, but a torture victim is.
Nevertheless, Shue is prepared to countenance the use of torture under extreme circumstances. He uses the hypothetical example of a terrorist who's planted a bomb that's about to go off. The terrorist has been apprehended by the authorities, and they need to know exactly where the bomb has been planted. But the terrorist won't play ball, so it's decided that he should be tortured to reveal the bomb's whereabouts.
Shue regards torture in these circumstances as justifiable because it's an act of self-defense. By refusing to divulge crucial information about the bomb's location, the terrorist is engaged in an act of war. Any subsequent torture inflicted on them, therefore, would be a legitimate act of self-defense.
Hill disagrees with Shue's analysis. While he claims that pain could be inflicted on a terrorist if they were actively engaging in some wrongful act, that would not apply in the "ticking bomb" scenario because a terrorist simply sitting in a prison cell is not actually doing anything.
Here, Hill makes a distinction between positive and negative duties. The terrorist has a negative duty not to do something, in this case blow people up. But torturing them to reveal the whereabouts of a ticking bomb would be imposing a positive duty on them, a duty to divulge the bomb's location.
According to Hill, torture as a means of self-defense would only apply in cases of negative, not positive duty, because then we would be protecting ourselves from the terrorist's failure to live up to their duty to blow people up.