A prank to the princess

As the new ruler of Eqestria, Twilight trotted into Canterlot, feeling confused but excited. But she focused on the task at hoof. She was getting Celestia and Luna a happy-retiring present. Well, she wanted to. Even though she knew the two sisters were her friends, she still had no clue what would be appropriate to get them. She glanced back and forth, looking for places to get a gift. All of a sudden, she spotted the perfect place. It was a . . .