Watch a video of actors Ethan Hawke and Gillian Anderson recall their experiences on Sept. 11, 2001. Ethan Hawke says: "At first I didn't believe that it was on purporse, I thought it was an accident." Gillian Anderson says: "In the history of X-Files, that was the only one day that they cancelled the day." She added "I won't forget it anytime soon." Watch the rest here.