When Timmy asks where his books/homework are, Sparky shows that he cooked it, and Timmy freaks out.
Poof says "Poop poop", then Wanda spits and starts to laugh with Cosmo. Chet Ubetcha also tells this joke during his news segment.
People talking about hot dogs, and eating them.
People mistaking doors as forcefields.
Someone saying that something is crying, when in reality it's the sprinkler splashing water.
In the title card of the episode, the "The Fairly OddParents in:" text remains throughout the entire duration of the title.
According to the end of this episode, Wanda doesn't like hot dogs because what is in them. Although in Odd Pirates, Wanda starts to take a bite out of one along with Cosmo and Poof as if she liked hot dogs. It is very possible that sometime between these two episodes, Wanda finds out what is in them, and therefore stops eating them.
When the rocket crashes into the hill with the Dimmsdale sign, it still says Dumbsdale, even though Timmy wished everything back to normal, so it should have said Dimmsdale.
When Timmy saying "Not now dad! I gotta think...I mean yes!" for a second his hat's top is gone.
Timmy says that his parents are even dumber than usual, but he only saw his dad be dumb.
When Timmy's Dad mistook the house door as forcefield for the first time, the doorknob inside the house was not aligned with the one outside. However, when it was shown the second time, it was put in the direction.
Mr. Turner is even dumber than usual, but before the wish, he was dumber than Timmy, so he originally have to stay dumb, just like Cosmo.
When Timmy asks, "Wait, where are my books?", the books on his desk are still there.