Do bubbles in Guinness go down?

Video clip 2

Clip 1 What can I see in this clip?

This clip is a more zoomed-in shot (about x6 magnification) taken midway up the glass.  Plenty of bubbles can be seen going down, and you can see bubbles of different sizes.  At about 2 seconds into the clip the bubbles slow down a bit and at about 3 seconds a dark wave of liquid (no bubbles) pushes its way in at the top left.  As in the first clip, this wave forces bubbles out of the way, dragging bubbles and vortices in its wake.  You can also see that this wave speeds things up quite a bit, and once it has passed (towards the end of the clip) the bubbles slow down again.  This shows most clearly that it is the dark waves of liquid that are forcing the bubbles down the inside of the glass.
AVI (3.9 MB)
Quicktime MOV (2.4 MB)

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(c) 2004 Alexander & Zare