At the spa, Rarity considers getting a new mane style, and an incident with an open window inspires her to try a moving style, much like Princesses Celestia and Luna. She tries many things, such as a spell from Starlight, hairspray, sticking her head out of a moving train, but none of them work. She eventually settles on simply having Spike use his wings to maintain a constant breeze against her mane, but even with his eagerness to always help her, he inevitably ends up fatigued.
I think it was interesting how, through the conversation between Twilight and Rarity, the moving manes and tails of Celestia and Luna are acknowledged. And of course, Rarity just can't face the reality that those two princesses are literally the only ponies in all of Equestria who are even capable of having such a thing. At least I got a few good laughs out of the montage of failures.