Deliberate mistake: When the Trunchbull is drinking from the glass with the newt in it, you can easily see that she doesn't actually drink anything, as the water level stays exactly the same. Logical, as the newt is real, but it's still very obvious because she drinks for about 15 seconds. (00:46:55)
Deliberate mistake: When the Looney Tunes are playing basketball against the aliens, if you look in the stands the same cartoon characters are in different places at the same time. This happens a lot.
Deliberate mistake: Practically all movies incorporate the name of the movie within the dialog. However, they must remember the English language and tense agreement. On at least two occasions, Fishburne says "Come on Dodge, lets FLED." If they were so interested in incorporating the name within the script, they should have named the movie FLEE.
Deliberate mistake: After Flipper knocks Sandy off the pier with his tail, there is an underwater close-up of the two of them swimming towards each other. This shot is flipped, note Sandy's watch and bracelets have switched wrists. (00:34:20)
Deliberate mistake: By the time the island blows up after Drax is destroyed, don't the explosions seem to move very slowly at the shot where Zane dives into the water?
Deliberate mistake: When one of the captains throws the grenade while Mason is in the bath, it coincidentally rolls to a left into the bathtub area, instead of rolling straight.
Suggested correction: The grenade isn't a sphere. It is obviously lopsided, and would tend to not roll in a straight line. Although it is probably exaggerated for the scene.
Deliberate mistake: In the scene where Joan and the kids pile into the station wagon after Stanley is kidnapped, Joan tells the kids to hold on tight and puts the car into reverse. However, in the matter of seconds that have gone by, Joan hasn't even started the car, yet she was able to put it in reverse and drive off. Even if she had the skills to start it that fast, you would hear the car turn over. The car is never heard turning on.