Coding of Facial Expressions of Pain in the Laboratory Mouse

For the purposes of this experiment, researchers injected mice with noxious chemicals, placed on them on hot plates, placed their tails in hot water, clamped metal binder clips on their tails, and performed various invasive surgeries on them without pain relief. Researchers systematically coded each mouse's facial expression on a "mouse grimace scale," concluding that mice do indeed feel spontaneous, emitted pain. According to the article, "This measure of spontaneously emitted pain may provide insight into the subjective pain experience of mice."