In Longing, Twilight takes Spike to the weather factory. When he sneaks some Rainbow Mixture, Twilight asks him if he ate it. Spike tries to prove that he didn't by breathing a bit of fire... Which is now rainbow colored...
In Halcyon Hearts, Shining Armor learns from Celestia that Twilight has finally gotten a boyfriend - a recently-paroled convict named Blaze. The story cuts to Twilight and her boyfriend enjoying their first proper date, and then towards the end of the scene:
Twilight: Do you hear something?
Blaze: No, why?
Twilight: I could have sworn I heard somepony calling my name just now...it sounded angry.
In "The Last Crystal Unicorn", Amethyst, who has a sweet tooth, starts gulping down a milkshake and gets a bad case of brain freeze. Eventually, the brain freeze goes away... He immediately drinks more and gets another brain freeze.