While she is speaking with Caleb about the test, Beatrice hears a train horn in the distance. How does she feel about the sound?

Beatrice feels as if the horn is Daunless calling out for her.

Our eyes meet. I hear a train horn, so faint it could easily be wind whistling through an alleyway. But I know it when I hear it. It sounds like the Dauntless, calling me to them.