After Antoine drops the Austrailan Rainbow fish in the tank, it gets eaten. When he places the fish's glass on the counter before he enters his bedroom, there is a fish in the glass.
At the fish store, Alison gets her entire chest wet, logo and all, while bending over to get something out of the tank for Deuce. In the next scene everything is dry except the immediate area around her breasts.
Near the end when Deuce Bigalow asks Allison (Fish Shop Clerk) for sea snails, she is wearing a flowered skirt, but when she goes to get the sea snails out of the tank, she's wearing the black jeans from the first scene.
When Deuce is being beaten up Claire, her shoes disappear for one shot. It happens just after he is kicked in the face three times to the music beat (still on at that time). When she does the spinning round kick she has no shoes on. After this kick they are back on again. It's only at the end of that scene that she takes them off asking Deuce not to tell Antoine about them.
When Deuce and Claire are fighting in Antoine's home, Deuce gets thrown into the middle panel of windows & knocks down the blinds. The blinds are alternately missing and back in subsequent shots.
If the seals were weak in the new fish tank the whole side would simply separate. The glass would not shatter.
Lionfish are poisonous to humans but when Antoine Laconte comes back to his home he drinks the Lionfish mixture; surely this would harm him in some way, but instead he just says "hmm spicy".
When Deuce and Fluisa are playing the food version of Trivial Pursuit, she says that peach cobbler is the pie with the most sugar. Pecan pie is literally made with nothing but pecans, straight syrup AND sugar added in.
The epilogue states Deuce And Kate Lived Happily ever after.
But She is killed in the sequel.
But She is killed in the sequel.
When Deuce and Carol are on a date at a restaurant, Deuce mouths her line "I've always wanted to try soup but there's the fear of drowning".
After Deuce and Kate leave the sushi restaurant, they walk to the end of the pier and he frees the fish that was going to be his meal. When he dumps the fish out of the bag into the "ocean," the splash is way too high and way too soon to have been the ocean below. The fish was dumped into a bucket or something held just below the camera line. Rob Schneider laughs visibly after this because the splash nearly hits him.
Right before Deuce destroys the apartment, he sticks a cheese sandwich, already toasted, into the toaster.
The treat Kate gives Bob on his birthday while he's fixing the toilet isn't really bibingka/bebinca, but just some sort of cup cake. The real thing is much more dense and sticky.
When Tc and Deuce are in the hot tub, if you look close you can see T.J.'s tomato fall out of his sandwich and into the hot tub. Then in the next shot, it's back in T.J.'s sandwich, then you see the tomato on Duece's chest.
At the baseball game, the crowd stands and yells something different than what Deuce and Ruth are mouthing.
When Tina and Deuce are walking down the sidewalk, you hear a woman's voice but the camera shows the bottom of her jaw not moving, showing she isn't talking.
Deuce reacts in amazement upon seeing a lionfish in Antoine's aquarium, and remarks that it's an $800 fish. In truth, lionfishes are quite common and their cost usually runs between $80 and $140.
As you can tell in almost every scene she is in, Kate clearly has two normal, real legs. Other than the bedroom "reveal", no effort was made by the filmmakers to convince the viewer that one leg was supposed to be a prosthetic.
At Kate's apartment, as Deuce follows the crying Kate down the hallway, he accidentally calls her by the actress's real first name instead of her character's first name.
When Deuce leaves the Alpha Beta Lambda sorority, Greek letters can be seen on the house, but the Greek letter for lambda is misrepresented as an "L".