Trivia: The combat simulation the X-Men are running on their first appearance in the film features the dread Sentinel robots. Originally, these were meant to appear in the second movie already, but the idea was scrapped. The simulation also bears a close reference to the parallel comic storyline and later movie X-Men: Days of Future Past, where the Sentinels rebelled against humanity, killed most of Earth's superheroes and erected a totalitarian regime in the US.