It seems that people aren’t the only ones who’ve learned to grin and bear it when faced with an unpleasant task: New study results suggest that even if horses act like they don’t mind body clipping, they could still find it to be stressful.

“Quiet acceptance (in well-trained horses) has been rewarded in the past and will tend to override their desire to escape and avoid whatever we are doing to them,” said Carol Hall, PhD, researcher and principal lecturer at Nottingham Trent University, in the U.K.

In a study led by Kelly Yarnell, a PhD candidate under Hall’s direction, researchers evaluated 10 horses (five described as “compliant” during clipping and the other five described as “noncompliant”) as they were “sham clipped”—meaning the researchers ran running clippers over the horses’ bodies, but the blades were not active. The researchers observed the horses’ behaviors, heart rate, salivary cortisol levels, and eye temperatures before, during, and after the sham clipping sessions. Thermographic eye readings can reveal instantaneous changes in stress level without touching the horse, unlike salivary sampling, Hall said.

True to their descriptions, the noncompliant horses showed more behavioral responses—moving around, resisting the clipper, kicking, etc.—than the compliant horses during the sham clipping phase and, to some extent, after clipping