In the world of Equestria Girls, the Humane Six can enter a "ponyfied" state, giving them pony ears and tails, along with a bunch of other stuff.

Normally, this went unnoticed even by Twilight Sparkle, the "woman of science" of the group, but when she sees Fluttershy in her ponyfied state, outside of a magical situation, she decides to check if prolonged stay in the form causes changes in the person's form.

Or maybe it's just an excuse to be next to Fluttershy, who knows?