Page 372 - Pinkie Face

Little do they know, Pinkie had planned for them to figure that out all along! Just probably not in that specific way.

Twilight Sparkle: Well, that was easy. Two turns and Cerberus has been completely pacified!
PM: Yep. You did it.
Applejack: Hmm…
Fluttershy: I don’t think Cerberus really wanted to hurt anypony. This could have gone very differently otherwise…
Twilight Sparkle: As fun as facing down a mythical beast was, I’m still wondering why Cerberus is in Ponyville. In Equestria, really.
Applejack: Ah’ve got a better question. Why has our happy-go-lucky PM suddenly developed a poker face?
PM: Mmph. What Are You Talking About.
(beat)
Twilight Sparkle: Tartarus. Cerberus being here means Tartarus is unguarded!
PM: PPFFFFF- Maybe.