Factual errors: When Martin and Beth leave Stathis Borans' home, he offers Beth the keys to his Jeep. The car they drive off in is actually a Chevy.
Revealing mistakes: When they try to revive Veronica after the childbirth, they shock her with a defibrillator. Someone holds her hand but doesn't seem affected by it.
Crew or equipment visible: When MartinFly throws Dr. Shepard's body, you can see a thick black string pulling it.
Audio/visual unsynchronized: At the beginning of the movie, when Veronica is giving birth to Martin, she is constantly heard screaming. But as the baby is born, reflections from the windows reveal that she has her mouth closed.
Continuity: Martin accidentally views a videotape of Seth Brundle, in which Seth explains his accidental fusion with the fly. However, although the footage comes from The Fly (1986), that particular discussion between Seth and Veronica Quaife was never actually videotaped, unlike the interview with Seth that Martin watches earlier in the film.
Audio/visual unsynchronized: When MartinFly sprays corrosive vomit in the guard's face, you can hear him scream even though his mouth is closed.
Crew or equipment visible: Crew guy visible under the table where chrysalis is opened.