"Because I need to thank them." He flexed his arms again. "This is awesome!" Miss Ethel's bubbly enthusiasm was coming to the fore again. "I won't have any trouble moving furniture now! OK class, I guess transformations are real! Should be interesting learning what it's like to be male, not to mention flying!" He picked up the fallen fragments of his dress and tied it around his waist, to conceal, barely, his new genitals.
The rest of the class was leaving for their next class, buzzing with excitement over their teacher's transformation (and in the case of some male-attracted people, more than just excitement.) Mary, hesitantly, stayed.
"Uh, Miss, Mister Ethel, that was me. I, uh, put these vials in your coffee."
"I thought it tasted funny! But seriously, Mary, you must never do that to someone without permission--that's what date rapists do! Show me the vial."
Hesitantly, Mary handed the vial to the massive wing-horsed man who had formerly been her petite female teacher. "What the heck" he asked in his deep, resonant voice "Is a 'werepegasus'"?