i dont really under stand it myself but they seem to pull the head in a side ways direction untill it looks like it gives up. the horse will remain standing for the half tap ,but the full tap moves the head and neck so far the horse lays/falls down remaining in what looks like a semi trance there is prob another name for it
if you read it all on his web site and see a lot of the videos he has made it is very good and has a similar effect to twitching on the horse it isnt cruel and he only uses it on very difficult animals where being kicked or bronked off is a serious problem he has great results it also helps with horses with feet handleing issues ect and the horses he works with are on the whole tb and its mainley th ecolts that are the sujects give it and open mind and watch