In the process of their investigation, the scientists in Osaka discovered that sperm from mice ‘blocked’ by chemical suppressants moved at the same speed as regular samples, but crucially lacked 'hyperactivation' – the distinctive swimming style that is caused by the sperm's tail beating at an extremely high frequency. The reason for this, they later found, was that without calcineurin the sperm was too rigid, an inflexibility prohibiting them from breaking through the membrane that surrounds the egg.