It can be shocking to hear stories about female terrorists like the Russian "black widows" and America's "Jihad Jane" -- particularly because women so rarely turn to violence. "We often turn our backs to the possibility that women could commit such hideous acts of violence," says Northeastern University criminologist Jack Levin. "We don't expect women to open fire ... and statistically they don't." As a result, many terror organizations have tried to use that element of surprise to their advantage.