I'm wondering how Pinkie whistled using a hoof. Somehow it's less weird that she can slow her dive than whistle without fingers.
Okay, Pinkie Pie's, uh, exuberance is so well known to the ponies that even her closest friends don't think the depressed one in sitting on the side filled with self-doubt is the real Pinkie?
Twilight making the Pinkies sit reminds me of a statement from the Discworld
series saying that dogs, no matter how they think otherwise, reflexively respond to a stern human voice telling them to "SIT!"