So while I was staring at her (I even changed my seat to have better view

In this well-known case the lady not only doesn't have any control of her feet, but also makes fantastic dangling show (provoked by herself!). But just look here:
The girls don't dangle because two of them are in boots and the third one - in heavily cut high-heel loafers, but their moves are still so aggressive that it drives me crazy. Especially the girl sitting in the right was very good in doing this, she have very fast feet, but still she is not as fast as the lady that I met yesterday!
However, the most of the craziest shoeplay shows are that ones with a lot of action. The more aggressive the feet movement is, the more wild is the shoeplay. Almost all good shoeplay shows that I have ever seen were made by ladies who had some troubles with controlling their feet while sitting

So, how should we called this fast up and down movements? For me "foot shaking" means something different - shaking is horizontal, not up and down.
And - the last point - do you agree with me that this is incredible sexy even if the lady doesn't dangle while doing this? This is very widespread habit and at the sime time very provocative behaviour - all people around have to notice it. I know that for some of them it is annoying, but for me it is so hot. And, what is the best, the lady probably is unaware what she is doing under the table
