Witnesses who are unable to communicate verbally are:

As per Indian Evidence Act, 1872- S. 119. Witness unable to communicate verbally. –– A witness who is unable to speak may give his evidence in any other manner in which he can make it intelligible, as by writing or by signs; but such writing must be written and the signs made in open Court, evidence so given shall be deemed to be oral evidence: Provided that if the witness is unable to communicate verbally, the Court shall take the assistance of an interpreter or a special educator in recording the statement, and such statement shall be video graphed.