You know, I'm surprised the show never comments on the fact that Twilight Sparkle learned the "little trick", aka hate magic, from just watching Celestia performing it once. Or that she performed it with obvious discomfort the first time (wincing as if in pain, trying to bring forth her negative emotions), but the second time it came completely naturally while she was upset (shooting at that stupid moving door in a second).
And of course it's never mentioned ever again after the end of the episode.
But you know... It's like a drug. Once you tried it... there's no turning back... >:3