It started with a trip to the basement of the American Museum of Natural History in New York to inspect preserved animal hides. Later, Georgia Institute of Technology researchers built a wind tunnel about 2 feet tall, complete with a makeshift eye. By putting both steps together, the team discovered that 22 species of mammals – from humans, to hedgehogs, to giraffes ­– are the same: their eyelash length is one-third the width of their eye. Anything shorter or longer, including the fake eyelashes that are popular in Hollywood and make-up aisles, increases airflow around the eye and leads to more dust hitting the surface.