When Jan Stevens is asking Billy to compare mouth sizes, Billy is eating a sandwich. This scene is shown mostly in a medium long shot focusing on the couch. After a close up of Stevens opening her mouth, it cuts back to a completely different take, noticeable by the shape of Billys sandwich, which now has way fewer bites taken out. It cuts back to the previous take with the nearly completely eaten sandwich a little later.
When talking to Lamina, Stone lets slip that Elle told him that she's secretive about food. But, at least in what can be seen in the movie, it was Billy who told him, and during Elles Interview, Lamina was listening at the door and would have known.
This could be meant as a manipulation tactic by Stone.