More boring seminar coffee cup experiments

The original video can be found here; you should watch it first. http://youtu.be/z1owFd28xWA

This video demonstrates how the coffee bubbles/droplets can ride the troughs between waves as long as the surface tension between the interface is stronger than the force of gravity on the bubble/droplet.

Anyone have any ideas on how I could determine if it's a bubble or a droplet?
This video was uploaded from an Android phone.

Видео More boring seminar coffee cup experiments канала Daniel Miller