The results showed that, in smelling the fear odor, horses had heightened fear responses, which caused them to reduce interaction with humans. Fear responses manifested through startle reactions, raised heart rates, and more staring at the “intruding” person. For example, the maximum heart rate of horses in the fear group was significantly higher than that of horses in the joy or control group. Horses sniffing fear odors also touched the participants less, stared more at the novel objects, and were more easily startled by the umbrella.

— Read more in Horses Can Smell How You’re Feeling at Nautilus.