This case recounts the story of a student who gave her cat half of a Tylenol tablet not knowing its potential harmful effects. The cat survives, but the incident motivates the student to learn more about the reaction mechanism underlying the liver toxicity of acetaminophen. The case outlines three possible reaction schemes that would explain the liver toxicity of acetaminophen-containing products. Students are required to write a detailed mechanism for each of the proposed schemes. This provides students with practice in writing both ionic and radical mechanisms, the two fundamental types of mechanisms covered in undergraduate organic chemistry.