According to witnesses on the plane, as it was reported by People, Grant Gustin went to the bathroom quickly after the plane went into the air, and it was shortly thereafter that a trail of smoke columned out of the bathroom door. It was then that the smoke alarm went off, and while there might've been a few passengers who put two-and-two together, there was also reasonable cause for concern as well. The pilots even put on their oxygen masks when the alarm went off; the smoke from the bathroom made it all the way up to the cockpit. Suffice to say, it became an ordeal.