Why can we know what is said in dreams without hearing the sound of speech?

The production of speech sounds requires certain conditions. First, the mind must have initial application and sustained examination (vitarka-vicāra) and wish to express something; then the wind touches the navel, and the breath follows from the navel all the way up, touching the throat and the tongue, and speech sounds come out. The loudness of the voice is related to the strength of the wind-breath; the strength of the wind-breath is related to the weight of initial application and sustained examination (vitarka-vicāra), to the intensity of the emotions of the manas and the consciousness accompanied by the five senses (pañca-sahagata-mano-vijñāna), and to the mental factors (caittas). In a dream there are only the eighth consciousness, the manas, and the solitary consciousness (mano-vijñāna-eka-citta); there is no consciousness accompanied by the five senses, and the body faculty does not function much either. Although the manas and the mind consciousness have the wish to express themselves, language and sound cannot be produced. Yet even without language and sound, one can still understand what the other person is expressing, because the manas can understand the thoughts of the other person's manas without needing language or sound. In a dream, the mind consciousness is not constrained by a physical body, so it has minor superknowledge; it can also understand the other's meaning, and can ascend to the heavens and descend into the earth.