Walking through airports, you've probably crossed paths with a few K-9 cops. But those dogs aren't just following their noses. They may be led astray by where their handlers think drugs and explosives are hiding, too—even when there aren't any. That's according to a study in the journal Animal Cognition. The researchers recruited 18 dogs certified by law enforcement agencies. As a test site, they used four rooms in a drug-and-explosive-free church. The researchers left the first room untouched. In the second, they taped up a sheet of red paper. In the third, they hid a few Slim Jims as a decoy. And in the fourth, they taped red paper to a stash of Slim Jims. The dog handlers were told they might encounter the scent of pot or gunpowder up to three times per room, sometimes marked with red paper. It was a flat-out lie—there were no target scents. But the dog teams still called 225 false alerts—most often at the site of the red paper, whether there were Slim Jims there or not. The study doesn't mean K-9 cops are totally unreliable in the real world. But it does imply that the dogs aren't immune to the power of suggestion—and neither are their handlers.