This is pretty neat, even in this very basic form:
Changing modes looks like it happens by magic, but from within the YouTube comments, the creator says:
Mode changing works by the eye tracker detecting eye glances, in this case a glance off the screen. So, a flick off the top gives you one mode and so on. The cursor changes to show what mode you are in, e.g pair of feet for walking. However, WoW takes control of the look of the cursor so it doesnt quite work. This was originally designed with Second Life as the testing platform, but we designed it such that could be used with other games. WoW was the first we tried and it works well for a start.
Nice job! Now to invent an eye-tracker that'll work at 5-10 ft; I could play WoW on the PC while reading a book on the sofa. This is the future, I tell you.