Which of the following is a sign of hypothermia?

Uncontrollable shivering is a significant sign of hypothermia, which occurs when the body loses heat faster than it can produce it, causing the core body temperature to drop. Shivering is the body's natural response to cold as it attempts to generate heat through rapid muscle contractions. This response indicates that the body is trying to raise its internal temperature.

In the context of hypothermia, shivering may begin moderately but can progress to uncontrolled levels as the condition worsens. If the body temperature continues to fall, shivering may eventually stop, which is a serious indicator that hypothermia is severe and requires immediate intervention.

The other options do not effectively represent typical signs of hypothermia. Severe headaches can be associated with various conditions, excessive sweating often occurs in situations of hyperthermia or heat stress, and a rapid pulse is more commonly associated with conditions like shock or anxiety rather than hypothermia, where the heart rate may actually slow down due to lower body temperature. Understanding these signs is crucial for life-saving efforts, particularly in cold environments.