The Subtle Knife
Spectres cannot be killed by any physical means, although numerous methods of countering their attacks exist. Angels can neutralise Spectres, and ghosts are able to hold them in combat. Humans whose dæmons have been removed from them via intercision can pass them without being attacked, and humans can repel them with the Subtle Knife. Stanislaus Grumman uses his skills as a shaman to control one and send it onto a church zeppelin to attack the pilot, causing the craft to crash. Mrs Coulter convinces a group of Spectres that following her command would give them more access to prey and is thus able to control them, and is able to make them "forget that they were earthbound" (so that they can fly). Consequently, at the end of "The Subtle Knife", Will and Lyra's guard of witches is taken by surprise and most have their Dust consumed by Spectres while flying.