That was the only reason Aaron was holding himself from shapeshifting into his wolf form in front of the girl. His inner alpha had been acting odd around the professor. If it was out, he did not what things would lead him to. And there it took him to, on the top of the girl, naked.
He had a hunch that his inner wolf was fond of the professor but to the level of cuddling, and playing with her was not definitely in his mind. When the professor fell over the root, whatever he felt rushing down his body was not an ideal, calm feeling.