Final answer:
A hypothermia casualty should not consume cold substances or use direct heat sources as it can worsen their condition. They should be warmed slowly, starting with the body core.
Step-by-step explanation:
A casualty suffering from hypothermia should not consume cold or alcoholic beverages nor should they use any sources of direct heat, such as hot water bottles or heating pads. This is because hypothermia is a condition where the body loses heat faster than it can produce it, leading to a dangerously low body temperature. Consuming cold substances can further decrease body temperature, and direct heat applications can cause burns or irregular heart rhythms if the skin and peripheral tissues are warmed too quickly. The important thing in treating hypothermia is to warm the person slowly, starting with the body core rather than the extremities to avoid complications like heart arrhythmia.