Pifias

When Beldar is reading out his fake security number, his bottom teeth are clearly human teeth. However, when Otto complains to Beldar that he needs to get his teeth fixed, Beldar has sharp teeth on the bottom.

When Gladys kisses Beldar in the car, his lips are smeared with lipstick. His lips are alternately clean/smeared in subsequent shots.

After successfully knarfling the Garthok, Beldar is suddenly covered with drops of blue blood. This is because a scene of him cutting of the Garthok's head was deleted. The head is still seen lying next to him on the steps in some shots (with the blue, bloodied stump facing the camera)

During Beldar's shower scene he is shown to have a flat, crackless rear end with two knob-like growths at the top. In a later scene when Connie is wearing a swimsuit she appears to have a standard human-looking rear without the knobs.

The mole on Prymaat's forehead disappears in some shots. This is most noticeable when she is speaking with Connie in her room.

Beldar and Prymat call the fried eggs "fried chicken embryos". However embryos are clusters of fertilized eggs, and the eggs we eat are not even fertilized. They should be called "fried chicken gametes".

Connie is wearing a swimming cap on top of her cone at the diving competition. Competitive swimmers wear caps because hair slows one down, but divers do not.

Connie is seen at a swim meet and in the next scene she is a cheerleader at the football game. High school students are not allowed to compete in two sports simultaneously.

When the car is lifted into the spaceship, cables supporting the car appear to be seen in a couple of shots, but this is the radio antenna on the car.

When they show the footage of 3 year old Connie on the beach you can clearly see the line of the conehead cap peeling off.

In scenes where the Coneheads still have their sharp alien teeth, Jane Curtin has audible difficulty speaking with the false teeth in.

When Beldar starts to pull back the roof of Ronnie's car you can see that the roof is already cut out underneath.

When Connie emerges from the diving pool, she is dry, even though she's blotting at her arms with a towel.

When the audience is pointing out where Beldar is hiding to the Garthok, it is noticeable they are wearing full, immobile face masks instead of elaborate make-up.

When Prymat shows Beldar the ad for a new house, she describes it as a "ranch-style", meaning one story. When the Coneheads move into their new home, it's a two-story house.

In the Spanish-dubbed version of the film shown on Spanish-language television, the Garthok's voice is left out; the monster opens its mouth and screams silently.

When Beldar comes home and sees all these candles on the ground, pay attention to the right of the screen. A crew member's hand is visible on the stair railing as Beldar walks past it.

For the first half of the movie, Beldar goes by an alias (Donald R. DeCicco) to work as an illegal alien. After Connie is born, he goes by the name of Beldar Conehead, yet can open his own business.

At least 16 years pass between the time that INS agents Seedling and Turnbull first hunt down Beldar and Prymaat until they encounter them again in New Jersey, yet neither of the agents seem to have aged a day older.

When Prymat sees eggplants while shopping, she screams in horror (likely due to their resemblance to her Conehead). Considering how much she shops (due to the large amount of consumption of mass quantities that takes place in their house) and the fact that it's been at least 16 years since the Coneheads landed, it's highly unlikely she had never seen an eggplant before.

Towards the end, Beldar offers Ronnie to take his car, because it is safer than Ronnies "shit box". Beldars car was taken to his planet while he and his family was extracted from earth, and when he returns to earth, he noticeably is not bringing his car back with him.

However. The Coneheads might've got a new car when returning to earth.