Cave rats make urine trails throughout the deep, dark caverns of the caves, which tell the rats how to find their way in the dark. | The size of a red blood cell is 708 microns. This is equivalent to one millionth of a meter. | Long Island is the largest island in the Continental U.S. | The most valuable painting made by a female artist is "In the Box," painted by Mary Cassatt. It was sold for $3.67 million at Christies in New York City. | Curly hair follicles are oval, while straight hair follicles are round.