Compression and expansion in Tai Chi Chuan

In class recently we were discussing the many ways to analyse tai chi chuan movements. One simple method is to observe compression and expansion, although one can also observe spiralling. In the sequence below, a variation of beginning style as an application, you can observe compression, expansion and spiral in both participants. its worthwhile studying the slide show, then perhaps follow the link, to a video version of the same move.
See the slideshow here (bottom right), and observe that compression and expansion is not merely through the legs, but involves the whole body..
See the video here

Click the picture to GO To the slideshow on the bottom right of the page above the video.