From Pluralpedia, the collaborative plurality dictionary
co-subvocalization (n.)
OriginScientific term

Subvocalization is characterized by minute movements of the larynx and movements responsible for speech, sometimes including the tongue and rarely lips, which occur when a person is reading or recalling words. Co-subvocalization may occur in some plural systems, whereby the same movements of the throat occur when a headmate is speaking via internal communication.