Jong Sau is indeed performed in the opening of the Wooden dummy, The hands form a triangle and both hands move forward together for optimum structural power,Deflecting incoming movements very well.

Worthy of mention is "BUE JONG SAU" which is the long bridge version of Jong Sau and is introduced in the first section of the Chum Kiu form. Bue Jong sau can be used to shoot into the opponents shoulder joint to utilize a type of "stop Hit" tecnique.(all very much based on angle structure and a type of slipping, while striking)

Jong Sau is Deflective in nature, bieng based on a triangle and is used as a bridge to contact the opponents bridge , continuing into a tan or bong, etc. This is a good example of Wing Chun's touch and go method, I.e. The hands do not "BLOCK" per se yet contact the bridge and flow into response counters......Hope this helps....

Regards , Sifu Lopez www.sillumwingchun.com