Chapter 50 contains a joke from Lauren about the stiffs procreating at the poker table. It originally started way back a long, long time ago in this little snippet.
The context of this has been lost to time, but I think this is from Tris's first few days back in Dauntless and after Lauren's issues at the fence.
Four didn't let her doubts seep in too quickly. He squeezed her fingers between his the entire way to the dining hall. He kept his hand on her back in line. He carried her tray and, even though she didn't ask for it, he made sure to get a slice of cake. He offered her the choice between Lauren, Shauna, and Derrick or Ro and Jordan. He slowed as they passed behind Lauren to squeeze her shoulder and comment into her ear, it was the only time his attention wavered from Tris. Lauren didn't miss her opportunity to take the focus back off of herself.
Four's hand had migrated around Tris's waist and to her opposite hip, positioning her close to his side with his shoulder behind her's.
"Oh God…" Lauren dropped her silverware.
"What?" Derrick didn't bother to block the view of his food while he spoke.
"The stiffs. Look at 'em. They're practically mating in the dining hall."
Shauna snorted and covered her mouth. Four rolled his eyes and Tris pursed her lips and turned red.
"Real nice." Four threw a pea at her.