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.

The actual heat of all the lights used on the set of Hypercube caused the black door portals to turn green, which is very noticeable on the portals on several occasions.