Ultimately, the dogs exposed to a stressed person’s scent were more cautious than the dogs exposed to a relaxed person’s scent. This suggests that dogs may detect differences in cortisol, or other chemical changes associated with stress and fear, via scent—even without training, says Parr-Cortes. Then, the dogs were exposed to the smell of a stressed or relaxed person before being given a new bowl. The dogs exposed to the stressed person’s smell were slower to approach the new bowl, indicating that the dog was less optimistic about finding a reward there. This effect was not seen when dogs were exposed to the smell of a relaxed person.