Quite an exciting area of one's advanced Tai Chi training and in fact any internal martial/healing arts training. This is where we learn about how the hands in particular work in activating and manifesting Qi for healing and especially for medical Qigong methods.
You never notice it when you see some advanced Tai Chi Master practice, however, one of his or her hands will be activating the Qi by moving over the Tantien in a certain manner while the other hand is manifesting that activation for healing on another person. This set was made at Erle Montaigue's annual summer camp in Rostock Northern Germany in August of 2007 over 5 days.
Please note this video was filmed by a student at the training camp, so the sound quality is not the best, but the information is not on any other videos, it's the only footage of Erle teaching this that we have.