Deliberate mistake: The signs at Dachau Concentration Camp are in English.
Revealing mistake: In the window there are already broken areas where the glass gets broken when Captain hits it. On the bottom pane the grill on the top, bottom and right have a crack before the Captain even hits it. (00:19:00)
Continuity mistake: Block 6 looks to have a no cardboard over the window beside the "Block 6" sign. Then later on they have cardboard there. (00:12:20 - 00:14:55)
Continuity mistake: The Block 6 door is closed all throughout the video, then when Captain runs towards the door it's opened. (00:07:55 - 00:14:55)
Continuity mistake: Becker is standing on the porch at "Block 6" and there are no handrails. When we return to Becker he is in the center of the square area and in the background handrails are there. (00:07:55)
Continuity mistake: The captain goes to "Block 6" which we see is the 1st floor with stairs which are in line with the porch, but when he leaves the stairs go off at a 90 degree angle from the porch. (00:04:50 - 00:06:20)
Answer: It's explained in the episode. The aliens are experimenting to see how humans react to various scenarios. This just happens to involve them using super strength.
Thanks. It's been a long time since I saw the episode so I forgot.