Days of Future Past: Part 2 - S1-E12
Continuity mistake: After Blob knocks Cyclops to the ground, Jean helps him up, and the two of them are standing a step away from Blob. The shot changes to Blob pointing and laughing for roughly a second, and when the shot changes again, Cyclops and Jean have disappeared, with not enough time to have moved offscreen. (00:12:20)