Factual error: The aliens request a meeting with Dr. Marvin on the shores of the Chesapeake Bay, near Washington DC. However, the shot of him driving along the shore line shows mountains in the background, which don't exist in Eastern Maryland.

Visible crew/equipment: Dr. Marvin decides to try out his new improved magnetic interference unit on a real alien spaceship that shows up outside the Belmont lab. As the truck with the device on it pulls up you can see the reflection of the crew in its door.