Mood Wings - Observations on Pegasus Body Language.

When Twilight Sparkle finds this book, she discovers an entirely new field of research. The secrets of pegasus wings lie before her, and she insists on making her own observations on the matter.

How?

Field research, of course.

Derpy Hooves is secretly a changeling.

Nopony particularly notices, or cares.

(New 9/15/19: Spanish translation by Spaniard Kiwi! Thank you!)