He starts to watch Hermione as well after he sees her lean slightly into one of McGonagall's lingering touches.
He quickly becomes aware that every move the Professor makes, is followed by a pair of dark chocolate eyes.
He wonders, if only for a second, if he should tell Hermione about what he sees, but decides against it in the end.
He would see how everything would unfold first, and step in if he needed to.
One lesson, Hermione is quieter than usual, so Harry waits for to see if their Professor picks up on it.
She does.
He follows her movements towards Hermione's desk.
He watches silently as his friend looks up from her work to McGonagall, and isn't at all surprised at seeing a new light in her dark chocolate eyes.