Of note, how close Rainbow and Twilight are touching (obviously close).

What better way to start this off? This is the scene where they first meet. We can all see when Twilight writes off Rainbow as nothing more than an 'all talk' pony and Rainbow proves that not only can she talk the talk but she can walk the walk. To me what really makes it is the end, the look on Twilight's face says more than I ever could.

And as a few have pointed out, Dash sounds a little nervous, like she's trying a little too hard to play it cool around Twilight.

Canon TwiDash