I already mentioned this briefly in the floorplan post, but it deserves to be its own post because I hadn't noticed it before that and I think it's really neat.
Throughout the series, we get several pretty good shots of Mark's split fishtank. The red fish is on the right (the side closer to the couch/TV) and the blue fish is on the left (the side closer to the front door).
However, when innie Mark is having his weird reintegration flash/hallucination at the beginning of 2.06:
We only see the left half of the tank (which would actually be the right side if we were seeing it from the other direction like usual). The two fish have switched places.
LIKE from a framing standpoint, having specifically the blue fish (blue for innie Mark, red for outie) in the foreground of this shot makes sense, but that could easily have been accomplished by just filming from a slightly different angle to get the other side of the tank instead. I love that this goes a step further than that - the blue fish is in the space normally occupied by the red one, and the kitchenette wall of MDR is clipping through Mark's house.
