. However, in many cases, the dogs in the control group that did find the treat appeared to sniff the floor until they were able to locate the treat. Perhaps they were following the scent trail left by the experimenter when the treat was placed in the room or were searching for any of the hidden treats using odor cues. This is an important possibility as, although it is heavily relied on by humans in police and quarantine work (Browne et al., 2006), the dog’s sense of smell remains poorly understood (Walker et al., 2006). Whether some dogs could discern the most recent scent trail left by the experimenter, even among the numerous other scent trails left by the same experimenter during the previous exposure phase, is unknown.