This clip is similar to clip 2, and taken slightly later in the settling process, but focussed slightly inside the edge of the glass. In this way you can see evidence that the bubbles further inside are going up, while the bubbles in front (and out of focus) are going down in front of your eyes. Although it is perhaps not immediately obvious, the dark waves (no bubbles) of liquid moving down in front are allowing you to see further in to the liquid to the bubbles behind. Lighting and timing for this shot was absolutely critical, and it took quite a few hours to get the perfect shot!