Night of the Sentinels: Part 1 - S1-E1
Revealing mistake: When the Sentinel is landing on the sidewalk, you can see the sidewalk is destroyed a split-second before the Sentinel's feet touch the ground. (00:02:05)
Starring: Alyson Court, Cathal J. Dodd, George Buza, Norm Spencer
Night of the Sentinels: Part 1 - S1-E1
Revealing mistake: When the Sentinel is landing on the sidewalk, you can see the sidewalk is destroyed a split-second before the Sentinel's feet touch the ground. (00:02:05)

Days of Future Past: Part 2 - S1-E12
Factual error: When Gambit is inside his mini-jet after escaping from Bishop and Wolverine, his radar screen says "Washington D.C." but the graphic above it is Washington state.
Days of Future Past: Part 1 - S1-E11
Trivia: After Bishop travels into the past, he hears one kid telling another that they will be playing the new Punisher game "Assassin." When the Punisher was first being developed, he was originally going to be called The Assassin.
Chosen answer: It says MPO "First Exemplary Printing House" which is a real printing company in Russia founded by Ivan Dmitrievich Sytin in 1889. There seems to be something about "named after..." as well.
Sierra1 ★