Halothane is a volatile general anaesthetic once used to sedate farm animals or reduce stress symptoms before handling and transport. Its use in swine is discouraged because genetically predisposed animals develop malignant hyperthermia, a potentially fatal runaway rise in body temperature, in response to the drug. Paradoxically, this dangerous reaction made halothane a diagnostic tool: exposing pigs to the anaesthetic specifically assesses halothane sensitivity, identifying stress-susceptible animals for breeding decisions. The episode illustrates how a pharmacological quirk illuminated a major meat-quality defect and reshaped pig genetics.