The Global FlyFisher
Simply the Best Place to go for Online Fly Fishing and Fly Tyinghttp://globalflyfisher.com/tie-better/whipfinish-video
A short video on using your fingers to whipfinish
I have now produced this small 40 second video, which shows the process from the angle of the tyer, and clearly demonstrates the ease of this finish. The video is hosted externally, and uses Macromedia Flash, so you will have to be abe to show Flash to see it. Most systems will have no problems.
As you can see the whole trick is to wrap the thread over itself. Even in the video it can be hard to see, but the principle is that you wrap the thread coming off the hook over the thread coming out of the bobbin holder while it's "catching itself".
Some tyers argue that using a whipfinisher - a tool - leads to nicer heads on the fly, but with a little care, your fingers will do an equally good job. I would even argue that the increased control and sensitivity of your fingers give you even better heads.
But first and foremost the advantage of using the hands is that you need no tool.