Redouble

In truth, a glass is never empty except in space, low pressure bell. Though it appears half full of water, the top half's occupied as well. In fact, the moment you add water, the glass begins to overflow. The air goes rushing out the top half, displaced by fluid from below. Air and water, life's two great pleasures; it's hard to choose between the two. When under pressure, forced together, refreshing seltzer comes in view! ---------- H/T to Milt's Rebuttal