rarity wears a disguise to hide her transformation into ponydragon.
digression:
Spike: You’re wearing a disguise again. It’s gonna have to be told sometime.
Rarity: but, um…
Spike: no you have to tell them. Besides I think fluttershy there already noticed.
Rarity: what? … but why didn’t she tell me?
Spike: I think she’s not who she says she is anymore.
I saw it stolen without flapping its wings repeatedly and the discord silence about us is too suspicious.
Rarity: you’re right discord that doesn’t disclose a secret is suspicious.
I couldn’t hide it very long with my pregnancy.
Spike: It’s safe with your pregnancy … your what?
Rarity: Yes with your mission, I forgot to tell you, but yes we are going to be parents.
Well, Spike just passed out.