My Little Pony: Friendship is Magic, Season 4

[Twilight is about to trade all her books for the broken quill a filly has

Pinkie Pie:
STOP!! What are you doing?

Twilight Sparkle:
I was trying to get rid of all the books I don't need anymore.

Pinkie Pie:
For that? Do you reeeeeeeally want that?

Twilight Sparkle:
Well, not really, but…I'm running out of library space, so-

Pinkie Pie:
Ohmygoshohmygoshohmygosh!! I can't believe that almost happened! But luckily it didn't happen, thanks to me.

Twilight Sparkle:
What are you talking about?

Pinkie Pie:
[showing a scroll] According to the rules of the Exchange, a trade is only fair if both ponies end up with something they want.

[Twilight rolls her eyes]

Pinkie Pie:
You can't break the rules!! Did anypony see you do it? I don't think anypony saw. But you are not gonna say anything, are you?! [giggles] Just kidding! [mischievously] Or am I?! Sometimes I can't even tell.