Other mistake: When the agent shows the spiral for the pattern of the messages, the spiral goes through South America and America. But the agent, before, showed two messages that aren't in the pattern; one in England (Stonehenge), the other in Cairo, Egypt.
Continuity mistake: When Rizzo is with the other lab rats and David Arquette says about having a funny boy, he bangs Rizzo's little yellow cap down on his head. In the changing shots, the angle of the hat alters about 5 times; sometimes it is on straight, then its half cocked to the side and at one stage it is on completely backwards.
Continuity mistake: In the scene with the Captain Alphabet messages, we see the words "watch the sky" being formed in a clear space on the tablecloth, but when Rizzo comes to look, the tablecloth is suddenly littered with cereal, many of the letters not even used in "watch the sky". When the words "are you there" appear, the tablecloth is once again clear.
Continuity mistake: Gonzo is eating an alphabet cereal for breakfast and aliens spell out messages. They tell him in one to "watch the sky" and there is a yellow toy plastic telescope that was in the box. Gonzo holds the telescope to his eye at one point but then he looks at a new message being spelled out and the telescope is shown back on top of the cereal.