Among the unsolved mysteries confronting 21st century physics from gravitational waves to dark energy, neutrinos -the "ghosts of the cosmos"- are near the top of the list. These awesomely low-mass subatomic particles, less than a millionth of the mass of electrons, play a key role in weak interactions and come three flavors: electron, muon, and tau. Stars actively flood the universe with new neutrinos along with ancient particles created some two seconds after the Big Bang. CERN announced this week that a muon-type neutrino dispatched from the CERN research laboratory near Geneva had arrived as a tau neutrino at the INFN Gran Sasso Laboratory in Italy, 730 kilometres (450 miles) away. It is only the third time that the mutation has been observed by the OPERA experiment, an international project launched in 2001 specifically to detect the bizarre change.