What metaphors are used in Proof by David Auburn?

When discussing where to go for Catherine's birthday in the flashback of four years prior, Catherine says she wants to drink Chicago beer "with no flavor." Robert uses the metaphor that the people who bottle the beer just get the water out of Lake Michigan to illuminate just how bland and flavorless it is. Of course, this is not the literal distillation process, but it is a vivid illustration of the beer's flavorlessness.