Without the behavioral timeline, this cat might have been sent home with supportive care until the infection advanced. Sickness behavior is not a side effect of illness—it is a central, evolved component of the immune system, written in the language of action rather than antibodies. For the veterinary clinician, learning to read that language turns every “quiet” patient into a communicator. And for the researcher, it dissolves the old boundary between neurology, immunology, and ethology, revealing a unified system where a mouse’s choice to eat or sleep is as precise a diagnostic as a white blood cell count.
