“The tongue in a certain state will cleave to the roof”

While looking for synonym comparison of “stick-cleave-adhere”, I came across this in English Synonyms Explained in Alphabetical Order:

To stick expresses more than to cleave, and cleave than adhere: things are made to stick either by incision into the substance, or through the intervention of some glutinous matter; they are made to cleave and adhere by the intervention of some foreign body: what sicks, therefore, becomes so fast joined as to render the bodies inseparable; what cleaves and adheres is less tightly bound, and more easily separable.

Two pieces of clay will stick together by tho incorporation of the substance in the two parts; paper is made to stick to paper by means of glue: the tongue in a certain state will cleave to the roof: paste, or even occasional moisture, will make soft substances adhere to each other, or to hard bodies.

What does “the tongue in a certain state will cleave to the roof” mean?

Solution 1:

I think they are referring to a human tongue cleaving to the roof of the mouth under certain circumstances. Originally I suggested this occurring when making a "tsk" sound but was rightfully corrected that in such a case it would not be considered "cleaving" due to the absence of a foreign body.

Solution 2:

I think CobaltDuck has the context correct.

the tongue in a certain state will cleave to the roof of the mouth

Consider that with the cited definition of cleave:

[the tongue and the roof of the mouth] are made to cleave and adhere by the intervention of some foreign body

I think the author is driving at: "You can force the tongue upwards and make it cleave to the roof of the mouth, close your mouth tightly so you jaw forces them together, or lodging something under the tongue can force it to cleave to the roof of the mouth."