Visible crew/equipment: As Ellie runs up the stairs of the observatory after hearing the first audio transmission from space, she runs towards doors with two large glass windows in them. As she opens the doors, a crewman/cameraman is visible in the right window for a brief fraction of a second.

Continuity: There's a scene where Ellie sleeps with Palmer, then gets up quickly to go to the lab. In her haste, she departs whipping on a shirt with no bra. The camera follows her outside where suddenly it appears she is now wearing one.

Factual error: When Mr. Hadden reviews Ellie's life history on his airplane, he says she graduated from MIT 'magna cum laude'. This is impossible, as MIT does not award academic honors to graduates.

Deliberate "mistake": The slew rate of the radio telescopes at the VLA has been greatly increased for the movie. They are actually quite slow and make little to no noise.

Continuity: If the cameras inside the Sphere won't work because of the magnetic field that is being given off by the machine, then why do the cameras on the main structure work?

Continuity: In the part of the movie where Ellie is traveling through the worm holes, in one scene it shows the restraint seat getting crushed against the top of the pod she's traveling in. However, when the camera shows Ellie inside the pod after she lands in the water, over her shoulder you can see the restraint seat in good condition. I realize some could argue that her trip never happened, but the special finding report, discussed at the end of the movie, proves her trip did in fact happen since her camera recorded 18 hours of static. Therefore, her restraint should have been crushed when the camera was showing it at the end of her trip.

Factual error: In the zoom-out at the very beginning, we hear broadcasts going back in time as we zoom out through the solar system. However, we hear broadcasts going back through time roughly 40 years. Shouldn't we be 40 lightyears out from Earth to hear them, rather than just in the Oort Cloud beyond Pluto? Radio waves travel at the speed of light like any electromagnetic wave. EM waves should not be confused with sound waves, which move much slower than the speed of light.

Deliberate "mistake": At the end, after Ellie testifies before Congress, she departs the Capitol building to a waiting limo. The media is there waiting for her. Behind the reporters appears to be the Reflecting Pool, and the Washington Monument at the far end of it. However, in reality, the Reflecting Pool is actually located between the Lincoln Memorial and the Washington Monument, not the Capitol.

Continuity: When Ellie drives back to the observatory after hearing the first audio transmission from space, there are several shots of her holding the steering wheel with her left hand while giving instructions to the other men. In one shot you see that the wrist-watch is turned upside down: the watch face is on the inside of the arm. In the following shot of her in the car the watch face is on the outside of the arm.

Continuity: When Ellie is in the pod and is talking to Kent, her monitor has the word "Hadden" in the top left hand corner. In subsequent shots, there is no "Hadden" on the monitor.

Continuity: When Ellie arrives back from her travels, the capsule lands in a net supported from four pillars, and to decellerate effectively, both the net and capsule end up in the water. However, when we view the splashdown from a CCTV camera (Cam 03) when Ellie is in quarantine, neither the net nor the pillars are to be seen.

Continuity: In the scene when the signal is first received, and they realize it is transmitting prime numbers, if you listen closely, the signal hits 11, starts over, but continues on up into the 30s, completely skipping all the prime numbers after 11.

Revealing: After the space pod splashes down in the ocean, it floats on the surface. But when they show Ellie from inside the pod after landing; there is absolutely no movement of the pod, and it's obvious the space pod is not resting on water. Even if it were hanging suspended in the air in the rescue net, its motion would still have it rolling around slightly after impact. But the footage from inside the pod shows the pod to be completely still without any movement, as Ellie asks how long she's been gone.

Revealing: During the scene when Ellie has discovered the Signal, and is in the control room with the guys, she turns to one of them and says "Make me a liar". Right when she turns, you can see some bright, smaller, roundish white lights reflected in her eyeglass lens. These are probably camera lights, as their appearance wouldn't match the computer screens or natural lighting in the room.

Continuity: When Ellie is being driven through the desert she sees The Preacher with the long hair. As it cuts between them, her seat belt goes from being folded to straight to being folded again over her right shoulder.

Continuity: When they realize the signal's counting prime numbers, watch the man in the red shirt behind Ellie when 11's being counted off. He's counting on his fingers, fills up his right hand, and moves to his left. The angle then changes to a closer shot, and his left hand is now curled up, with no numbers counted off on it at all, and he continues on his right.

Revealing: During the scene when Ellie is traveling through space, she unbuckles herself from the chair to retrieve the compass. The chair then breaks off from the violent movements of the space pod, and slams up against the ceiling. At this moment, Ellie is in deep space in a completely weightless environment. She is floating, suspended in the pod and the chair itself floats a bit before being slammed upwards by the force of the pod movement. But, some small parts of the chair (bolts, etc.) are seen falling directly down, towards us in obvious full gravity; revealing that the scene was actually shot in normal gravity. Oops.

Continuity: When the Machine is used for the second time (with Ellie in the pod) the large outer ring is set spinning. This brings the total number of spinning rings to three. However, when video of the pod falling through the machine is played back on the T.V. screen, the outer ring is fixed horizontally and not moving at all. Only the two inner rings are spinning.

Continuity: During the scene in which Ellie is preparing to go in the pod through the alien machine built in Japan, she puts a small digital video camera on the side of her head (with a headphones-type headband holding it in place). During subsequent shots of her in the pod before it drops (and there are many from different angles), the camera's orientation changes noticeably from shot to shot.

Plot hole: During the Congressional hearing, it is suggested that the alien signal could have been faked from a satellite - as Ellie only has her own experience to go on, it leaves her believing what happened, but still with an element of doubt. However, as a professional astronomer, Ellie would have immediately dismissed this since a simple parallax (triangulation) would have confirmed that source was at the distance of Vega - a distance far too great for any rocket to reach. (This is mentioned in the book).