What is the principle behind quenching thirst by looking at plums and salivating when hearing the word 'plum'?

What is the principle behind "quenching thirst by thinking of plums" and salivating at the sound of sour plums? Without drinking water or eating anything, the problem of thirst is solved—who solved it? When one is thirsty, there is no saliva; when there is saliva, the mouth is no longer thirsty. How does the saliva appear? The brain issues a command, transmits it to all parts of the body, or to a certain part, and a certain reaction occurs. Who issues the brain's command? It is issued by the manas; the tathāgatagarbha executes the command, supplying what is needed, satisfying the manas, and fulfilling the manas' aim. Therefore, if the manas had no desire, could states of experience appear? No state would appear at all, and no change would occur at all.

Why does the manas, upon hearing about sour plums, cause sour water to be spat out? The "hearing" here is, of course, the hearing of the ear consciousness and the mind consciousness, which then transmits the information to the manas, and the manas thereby knows about the matter of the plums. Knowing that the plums are sour, knowing what the nature of the plums is—is this known by the mind consciousness, or by the manas, or by both? Based on past experience, having known the nature and function of the plums, one's imagination runs wild, as if the plums were really in one's mouth. The manas is deceived and misled, and it causes the material body to produce the corresponding reaction; the sour water then appears in the mouth, and thus the problem of thirst is temporarily solved.

From this we can see that when the mind consciousness engages in non-valid cognition and discernment, and the manas does not know it is being deceived, abnormal phenomena appear. It is evident that throughout beginningless kalpas, the mind consciousness has not seldom deceived the manas, and then the manas in turn makes things hard for the mind consciousness.

The solitary consciousness (mano-vijñāna-eka-citta) imagines itself standing at the edge of a cliff, and so the soles of the feet feel numb, the whole body trembles, and out of fear of falling, it tightly controls the body faculty, tensing it up. Who caused this? It was caused by the manas, as the result of the tathāgatagarbha initiating and cooperating. Because of the mind consciousness' attention not in accordance with reality, the manas' attention not in accordance with reality arises, after which erroneous emergency measures and commands are issued, and abnormal reactions of the body faculty appear.

Throughout beginningless kalpas, the mind consciousness' false instruction of the manas has caused the manas to keep walking along wrong paths, unable to return to the correct path. The mind consciousness' false instruction is the result of being directed by the manas' ignorance and delusion. If the manas had no ignorance, the mind consciousness would certainly always be enlightened, and there would be no wrong views and false views (mithyā-dṛṣṭi) or false instruction, and the manas would likewise never have wrong views.

You deceive me, and I deceive you—this is cause and effect (karma). You are deluded, so I am deluded, and then I make you deluded again—this is cause and effect. Therefore, the cause of the transmigration through the three realms and six destinies, the cause of birth and death, is the manas' ignorance. And the manas' ignorance has existed since before beginningless kalpas, stored in the tathāgatagarbha, enabling the tathāgatagarbha to give birth to birth and death—this is what makes the cycle of transmigration suffering.