That Sleeping Bear Knows You're There

“Hibernating bears are more alert than they appear, according to a study showing that their heart rates increase in the presence of a silent intruder even though they appear to be fast asleep…. One of the most intriguing discoveries was that hibernating bears appeared to be aware of humans approaching their winter dens even when every effort was made to ensure that the sleeping bears were not disturbed by any loud noises. Their heart rates increased in preparation for a sudden attack.”

Photo by Anan Kaewkhammul, via Shutterstock