During the entire dinner scene, the amounts of wine in the glasses change several times.
At the end of the film Jack says that he has around 20 minutes until the cake is cut. However, shortly after this the cat and dog are shown eating a piece of cake. The cake is then shown to be uncut.
When Mr. Jinx lets Little Jack out of his playpen, the gate is left open. However, in the next shot when Moses the dog is chasing Mr. Jinx, the gate is shut and properly locked. In the next shot, the gate is open again.
The amount of whipped cream on Bernie's face changes between shots, even after he has stopped wiping it off with the towel.
When Jack meets Greg's "supposed" son at Isabel's home for the first time, Jack alternates between having his arms crossed with his hands on his hips between shots.
Sodium pentathol works as a truth serum in that it relaxes a person and does make them very communicative, sharing thoughts without hesitation. This makes them easily guided in questioning since they speak first and think later. However, the person loses inhibition but not self-control. The person will not simply begin to spill information if they choose not to or are not prompted to do so. Sodium pentathol is also a commonly used anesthetic. A syringe with a highly concentrated dose of that amount would have put Gaylord out cold on the floor. He wouldn't have been awake enough to tell the truth.
Greg is clearly driving the motorhome on the interstate with two divided pairs of lanes going in opposite directions with white (not yellow) lines down the middle, yet one shot shows an SUV going past them in the opposite direction in the lane right next to them (and they're all in the wrong lane, too, for America).
Although it is understandable that the County Judge released Greg, Bernard, and Jack from jail, it is generally not appropriate for a public servant to grant preferential treatment, like the Judge clearly did (Roz saved the County Judge's marriage, and this is clearly the reason why the Judge has ordered the guards to open their cell.)
Florida vehicles do not have front license plates. The sheriff car has front license plates.
After Jinx escapes from Jack's grip to chase Moses, Jack exclaims "Jinx!" However, the subtitles say "Jesus!" instead.
In Judaism, the circumcised foreskin is buried in the ground, yet Greg's parents keep his in a scrapbook. This is more than likely an example of their eccentric behavior, and the fact that they are overbearing and chronicle ridiculous moments of their son's life.
When Greg picks up the brick to throw at the RV, the audience can clearly see it "compress" in his hand, showing that it is made of sponge, not real brick.
When Little Jack is discovered to have glued his hands to the rum bottle, a string and possibly some tape are visible holding the bottle to his hand.
When the camera cuts to a wide shot of Greg and Bernie Focker handcuffed on the cop car right after Jack Byrnes turns around his RV, Greg's handcuffs are open even though he has his hands behind his back.
LJ's body double, a doll with completely different colored hair is seen in at least two shots. One in the trailer, when Jack is explaining the feeding process and the other, when he is supposed to be sleeping in the crib.
When Greg is by the awards that Roz and Bernie have displayed for him in the kitchen (Bernie is at the island in the kitchen), the name on the plaque is clearly spelled Gaylorck Focker instead of Gaylord Focker.
When jack injects Greg with Sodium Pentothal, he uses an IV needle, but injects him via intramuscular route.
When the minister is playing the wooden flute at the wedding, the pipes he blows are clearly unrelated to the sounds being produced (low notes vs high notes). Also, his mouth moves to other notes on the flute while the previous note continues to be heard.
When Bernie is going to fight with Jack, Jack warns him that it would "bring his demise". While Jack is speaking the camera is shooting over his left shoulder and it can be seen that Jack's mouth is not moving.
When Greg wakes up in his parents' bed, he holds the note left for him by Jack. Although he's holding it perfectly still, you can hear the sound of crackling paper.
When Jack and Little Jack are driving off in the RV, the reflection of the camera crew is visible on the outside of the vehicle.
The trees shown lining the streets of Chicago do not grow in Chicago.
The marina where the engagement party occurs is clearly not in South Florida. The super-tall Mexican Fan Palms seen in front of the building do not grow that tall in the hot, humid climate of Miami.
In Chicago the street signs are green and not blue.
When Greg is on the phone with his father he tells him that his flight lands at 7:30 however when he prints his boarding pass it shows a different arrival time.
The Fockers moved to Florida shortly after Greg's grandparent passed away yet the room that Greg and Pam stay in is dressed up with drums and posters as if Greg lived there growing up.
Roz Focker says that "they're probably down in in Little Havana having chimichangas." Little Havana is a renowned Cuban area and traditional Cuban food does not include the Mexican dish of chimichangas.
There is no Latvian naming tradition like the one Gunther describes.
In the first film, Pam tells Greg that her father had been in the CIA for 34 years. However, in the jail scene towards the end of the movie, Jack tells Bernie that he was in the CIA for only 32 years.
At the wedding, Bernie mentions having been Greg's father for 36 years. But one major plot line revolves around Greg being 19 when he lost his virginity, and that this happened exactly 15 years ago. If Greg was 19 years old 15 years ago, this would make him 34, not 36.
The girls on the "horny" bus have a banner that exhorts drivers to "Honk if your horny," instead of "you're."