Mouth slit

What ArcHivist Hegelia termed the mouth slit was the equivalent of the humanoid mouth seen on the faceplates of certain subspecies of Cybermen. (AUDIO: The Early Cybermen)

The Cybermen produced by Cybus Industries in Pete's World had mouth slits which gave off blue light whenever they spoke. (TV: Rise of the Cybermen et al.) Similar Cybermen appeared in N-Space. (GAME: Blood of the Cybermen, TV: A Good Man Goes to War et al.)