What is rigor?

Rigor refers to violent shivering that occurs during a fever, which often accompanies a sudden increase in body temperature due to infection or illness. This response is a physiological mechanism that reflects the body's attempt to generate heat and raise its core temperature in order to fight off pathogens. When fever occurs, the hypothalamus in the brain resets the body's thermostat to a higher point, which can lead to chills and shivering as the body tries to reach this new temperature.

The other options describe different physiological sensations or conditions but do not correctly define rigor as it relates to fever. Sensation of cold temperature is not specific to the shivering mechanism associated with fever, while a slow and steady heartbeat is unrelated to the shivering response. Increased sensitivity to light also does not relate to the described violent shivering. Thus, the correct understanding of rigor as it relates to fever is crucial for recognizing this important physiological response.