You're an artist, and artists generally have the same weaknesses, I've come to find. [He glances down at her hand before motioning to it.] No nicotine stains on your fingers, so it's not cigarettes. [His eyes travel up her arms to her face.] No track marks that I can see, or any other evidence that give away that you drink or use drugs, except maybe on a social level.

So, that leaves sex and caffeine.

[Sure, they may have sounded more like assumptions, but Caius hadn't spent as long as he had observing people to consider them as such.]