Too close for comfort

During the examination, the patient described feeling as if an unknown person was standing behind her, mimicking her body position. "This person is standing behind me, almost next to my body, but I don't feel it," she told the doctors, who described the discovery in the latest issue of Nature.

When asked to lean forward and hold her knees, she reported feeling as if someone behind her was hugging her—a feeling she described as unsettling. While following instructions, such as trying out cards for a language game, she said the shadow tried to get in the way. "He wants to take the card away from me," she told the doctors. "He doesn't want me to read it." Like schizophrenics, the patient was unaware that she was experiencing a body illusion.

"She might have understood that [the shadow] was an illusion, but she didn't," said study co-author Stephanie Ortigue, a neuroscientist at Dartmouth College in Haonver, UK.