The Elements of Harmony. They're the key to saving Equestria. At the end of the day, Twilight needs the keys her friends have acquired over the past few months of hard effort. For Fluttershy, Rainbow Dash, Rarity and Pinkie Pie, their keys are somewhat normal. But Applejack's key is a bit. Or rather, it was... She traded it for something else.

Something intimate.

Something like a condom.