A 3D filming technique has revealed that human sperm really swim with a corkscrew motion like otters, rather than wiggling like eels due to their'wonky tails'. Developed by scientists led from Bristol, the method has overturned a 350-year-old belief that sperm tails lash'with a snakelike movement, like eels in water.' In fact, the researchers said, this is merely an optical illusion -- one that is a product of seeing the motion under standard, two-dimensional microscopes. Seen in three dimensions, the reproductive cells instead clearly rotate like a corkscrew as they strive to journey towards an egg. The findings could help to better understand and address the causes of male infertility -- which is thought affect around one-in-seven British couples. A 3D filming technique has revealed that human sperm (pictured in this artist's impression) swim with a corkscrew motion, rather than wiggling like eels due to their'wonky tails' 'With over half of infertility caused by male factors, understanding the human sperm tail is fundamental to developing future diagnostic tools to identify unhealthy sperm,' said paper author Hermes Gadelha of the University of Bristol.