When a conversation becomes sufficiently complex and ecstatic, its participants may experience psycho-optical phenomena. That is, the mind's eye may observe shimmering, static, moiré patterns, or others. We believe this occurs when the logical interrelation of the ideas at hand replicates that of physical objects which produce these effects visually.
For example: A raft of considerations might organize itself in a logical lattice. A subsequent conceptual grid might mirror the first, adhering to a parallel logic. But the latter grille may fall farther from the thinkers along a certain conceptual axis -- and now we have established the misaligned grids which characterize moiré. This pattern is a refraction of thought, which seems to flow like light.