Continuity mistake: At the end of the episode, Fluttershy reveals that she still has a fang left over from when she was a bat pony. This wasn't carried over, and her teeth have been normal since.
Continuity mistake: During the "Stop the bats..." in the song, Rainbow is shown behind Flutter-shy, but when she walks in front in the same shot, the mane colours are swapped.
Other mistake: During the song, as the cardboard tree falls, Apple-Jack lifts her hoof in a way it couldn't possibly bend.
Continuity mistake: During the song, a bat spits out an apple that falls on its side. In the next shot, that same apple is upright.
Answer: The smoke floats a few feet away from Twilight and close to the camera so you might think that the smoke is right in her face.
Lily Harrison