What word is defined as "the silent movement of the lips in simulation of the movements made in audible speech"?

In the 2001 novel, "At Swim, Two Boys" by Jamie O'Neill, he wrote the line: "... not the conversation by any civilized standard, but a kind of mussitation, the prisoner's half-mime half-whisper, under the nodding eye of an orderly." Thus, the word mussitation is being applied by O'Neill as it is commonly defined. It is used to mean the silent movement of the lips in simulation of the movements made in audible speech (muttering; mumbling; or murmuring).

Mussitation is a very rare noun which derives from the Latin word mussitātiō (to speak in a low tone, grumble, take no notice of, bear silently). In a modern medical sense dating from the late 19th century, mussitation has focused upon the actions and the sense of people “moving their lips in silence as if they were speaking”.

The word mussitation is considered to have directly entered English speaking countries in the mid-17th century.