Detected in 1977 by the Big Ear telescope, the Wow! Signal remains an iconic SETI mystery. Jerry Ehman famously circled the sequence "6EQUJ5," which matched the 1420 MHz hydrogen line and lasted 72 seconds. Though it never repeated—sparking decades of alien speculation—new research proposes an astrophysical cause: a rare maser flare from a hydrogen cloud stimulated by a transient radiation source, such as a magnetar flare or soft gamma repeater.