In the videos, caged monkeys are approached by a lab assistant who makes a variety of threatening moves, testing how the macaques respond to stress. These actions include making eye contact with the monkeys—an aggressive gesture for macaques, according to The Macaque Website managed by the U.K.’s National Centre for the Replacement, Refinement and Reduction of Animals in Research. The macaques respond by running around their cage, flinging themselves at the bars, making loud noises, and exhibiting submissive facial expressions. These are understood to be fright responses.