When Kate and Sasha are talking and Kate says "Please, you have to have some idea what this means.". At that time you can see an alien looking person moving reflected in the walls. It moves into view, stops for a second and moves out of view again. This is not Kate because she is standing on the other side of the room. There is also a quiet sound effect as it shows itself. See more...
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Revealing: The way Jerry comes into play is problematic. He is shown coming up from the bottom of the room where Kate has just met Sasha. He appears to be climbing upwards, which suggests that the gravity in the room that he is leaving is the same as the one that he is entering. However, the way that he positions his body around the square opening doesn't make sense. He turns around to see the girls. At this point, it would be very difficult for him to stay up, because he no longer has support like he did when he first came up. This shows that the actor was standing on something.
Other: In the second scene, where we see the colonel, he is looking through a door to another room. After the door closes, we see that he was looking down, into the room below. But, as we saw in the previous shot, his tie was not dangling downwards as it should have been. It wasn't a Gravity Shift, as he never entered that Cube that the camera was in.
Other: This occurs during the scene where the group has just rescued the colonel. Before Mrs. Paley makes her appearance, the others notice the panel opening, and make movements, but they don't make sense. We'll call the side where the colonel was the north. Sasha is in the southwest corner, and Max is near her. Simon and Jerry are both at the north wall. When the sound of the door opening is heard, Max looks to the west. Simon is kind of in a strange position, but looks correctly to the north, where Mrs. Paley comes from. Simon and Jerry both knew where to look before the door opened, so it's reasonable to assume that it's easy to tell which door is opening, so Max shouldn't have looked at any other door.
Continuity: When we first see the colonel, he grabs the suitcase to examine it. In the far shot, you can see that the handcuffs are on the far side of the handle, near his body. The next shot is a closeup of the suitcase, and the handcuffs are now on the opposite side of the handle, away from his body.