SPOILER: What were THEY doing in 'The Flash'?! An explanation of all those crazy cameos

The new Ezra Miller-starring superhero movie "The Flash" follows the titular and super-fast hero on a time-bending odyssey that literally sees "worlds collide" just as the tagline suggests, in a jaw-dropping climactic sequence showing various alternate-universe versions of certain DC mainstay characters. It's sure to thrill some, while others will be left scratching their heads.