After the aptitude test yesterday, today is the Choosing Ceremony where the 16-year olds actually get to choose their faction. (The ceremony is held at the Hub, which we used to call Sears Tower, though now it's called Willis Tower, which is probably what brought on the disaster that led to Beatrice's world.)
And just to remind us what Abnegation is all about, all the Abnegation folk take the stairs so that others can take the elevator.
At the ceremony, each 16-year old gets cut and puts some blood in a bowl symbolizing one of the factions: the bowls are filled with "gray stones for Abnegation, water for Erudite, earth for Amity, lit coals for Dauntless, and glass for Candor" (11).
Marcus gives a speech about democracy and choice and yadda yadda yadda. He explains that each group blames evil on some aspect of human personality, so they organize against that part: Dauntless blame cowardice, Candor blames lies, etc. You get the gist.
Caleb goes before Beatrice and surprises everyone by choosing Erudite. So now Beatrice feels like she can't abandon her parents… but she chooses Dauntless anyway.
Actually, first she spills some of her blood between the Dauntless and the Abnegation bowl, which is a scene that should have a giant neon sign over it that says "symbolism."