Rarity discovered the location of the mirror pool that Pinkie had used, she asked Pinkie how to use it, and cloned herself several times. Applejack is very upset about this, and the sheer numbers of Rarities is too much for the poor farmgirl to handle. And then it dawns on her, she could kill all of the clones, but she would have to be quiet about it, so not to arouse suspicion…