Hibernation is when an animal is in a dormant state for a length of time. Animals hibernate during winter. Some animals will hibernate for the whole winter season without waking up once. Other animals will wake up as often as once a week to get rid of waste and to eat. When an animal hibernates its body temperature will go down very low, only a few degrees above the outside air, some animals' body temperature wil go down below freezing point. During hibernation an animals' heart rate and breathing will be very slow. Some animals heart will only beat five times per minute and they will breathe only once per hour. Animals that hibernate usually weigh less than twenty killograms. Some scientists do not believe that bears truly hibernate because even though their breathing and heart rate go down, their body temperature drops only a few degrees. Also bears weigh way over twenty killograms.