[He watches this demonstration studiously. The lesson is obvious, even understood, and yet...]

Then why different names? One cannot be 'full' and 'empty' at the same time. [He turns one bottle side-ways, following Mark's hand movements.] The same amount of water. I put it all there myself, drop by drop.

Yet now I find myself at a paradox of terms of a philosophical nature. If we, perhaps, extend some spirituality to this liquid, then perhaps one could be construed as empty.

[This is a new concept and requires a moment of silent pondering.]