When Jake is about to convert the gold bar, we first see him seated in the middle of the couch, 'concentrating' on the bar in front of him...when the military bursts in to the apartment, the shot is wider, and we can clearly see that Jake is not on the couch, but it then immediately cuts to a shot of him on the couch again.
Early in the film, Frank and Jake discuss procuring the bar of gold necessary to repair the ship. During the discussion, Jake says that he will need to reduce it while retaining all its properties. Later, when Jake reduces the gold to the size of a small pencil, Liz easily picks it up. If the "reduced" gold had retained all of its original properties as Jake said, it should have had the same mass as a bar of gold.
Stallwood (Roddy Mc Dowall) films the house using an 8mm cine camera. Although he might have been able to take it to a laboratory that could process it the same day, when the film is being projected an Academy trailer has been spliced onto the end of the film, which isn't used on 8mm film.
In the early scenes, when Jake the cat is demonstrating the light-up collar's power to Frank, you can sometimes see the two thin power wires connected to the light up collar running along side of the cat.