" He could see faint streaks of light as if the man left behind prints. They didn't appear like footprints, there were more faint bluish lights, more of a blob-line than a print, but every person left them behind and from shadows he could see them. He couldn't spot the imaging once out of tube, but the shadows acted as if he was seeing through a thermal lens. "

― Christine Feehan , Shadow Warrior (Shadow Riders, #4)