When Orville and Dr. Orvilla are having a slapping fight Dr. Wilson walks in and stops them. Dr. Orvilla is holding a briefcase but in the next shot Orville is holding the briefcase.
They actually go to Venus.
At the end, Orville's space helmet is full of water in the longer shot, but in the close-up, it is suddenly also full of fish.
When the rocket enters the Lincoln tunnel, it enters on the right side of the tunnel. It exits on the left side of the tunnel.
During the scene in which the rocket is flying in space, just before they land on Venus, when the rocket is flying by, you can see the string holding it.