Horowitz was able to show that the human tendency to attribute a "guilty look" to a dog was not due to whether the dog was indeed guilty. Instead, people see 'guilt' in a dog's body language when they believe the dog has done something it shouldn't have – even if the dog is in fact completely innocent of any offense.

During the study, owners were asked to leave the room after ordering their dogs not to eat a tasty treat. While the owner was away, Horowitz gave some of the dogs this forbidden treat before asking the owners back into the room. In some trials the owners were told that their dog had eaten the forbidden treat; in others, they were told their dog had behaved properly and left the treat alone. What the owners were told, however, often did not correlate with reality.