https://phys.org/news/2018-07-calmer-horse.html

"Horses can be under a lot of stress, so I was interested in seeing if aromatherapy could help in reducing stress," said Chea, who had never been around horses before taking Baldwin's course, Physiology of Mind Body Interactions, at the UA in Tucson, Arizona.

During the class, Baldwin uses horses to teach students about heart rate and heart rate variability, which is a measure of the variation in time between each heartbeat. Both are indicators of the level of stress a person or animal is experiencing, though heart rate variability is a much more sensitive measurement.