The popular religion of China is a trance-medium tradition. There are many variations of this. In some places an individual within a locale, will be the only person who becomes possessed by the local deity. He or she may channel the voice of the deity, may physically embody the movement of the deity, or may violently black-out and then recount the visit from the deity after waking up.
Some mediums are also adept at channeling multiple deities. If a new person becomes possessed by a known deity, villages have a mechanism for determining if the possession is really the deity it claims to be or an impostor. Possession has always been one of the ways to challenge authority. One of the ways of determining the authenticity of a possession is to observe how the eyes are used.
Mediums were so pervasive in China that the government certified certain mediums to testify in court on behalf of the recently murdered. One of the first signs that a medium is going into trance is a change in the eyes.
The term Daoshi (sometimes translated Daoist Priest) is like so many Chinese terms in that it has more than one meaning. One of its meanings is, an expert at identifying the type of Qi involved in a trance, a possession or even an entire cult. Detailed descriptions of Deities, spirits, demons, and ancestors were collected into books called Registers.
At the risk of over simplifying, we could think of a collection of Registers as sort of a cross-referenced Deity phone book. A place where a Daoshi could look up all the characteristics associated with a trance and find a match. The sounds one hears, the claims made by the channel about the deity, colors and smells described by those present, the physicality of the movement, the emotion, and the look of the eyes, were all details which could be cross-referenced to figure out what type of deity was present, how powerful it was, how dangerous it was, how it could be controlled, negotiated with, or appeased.
Part of the training to be a Daoshi is to actually practice all the different ways of going into trance, but never falling into full on possession. It is again, a practice that teaches you what not to do. Obviously a key part of this training is learning all the different things that can potentially happen to your eyes, or your gaze, as you fall into trance.
This little bit of Daoism, is part of the teaching of each of the eight mother palms of Baguazhang.