As they were headless, the Headless Monks did not register as living beings. They were also supposedly incapable of being fooled or surprised or of feeling fear. Despite their lack of heads, the Monks were able to detect where other beings were. They could fire energy blasts from their hands, as well as channelling that energy into the swords they carried. They could be killed just as easily as most other humanoids, with energy blasts, guns, or sword wounds. They also had some form of vocal ability, as they could chant, though this may have been a psychic ability. (TV: A Good Man Goes to War)