1.5. Non-manuals
Lexical non-manual features are organized in three categories: mouth gestures, mouthings, and other non-manuals such as facial expressions, and movements of torso or head. The non-manuals described in this section are obligatory properties of lexical items, probably except mouthings. So, their function is purely phonological, in other words, the sign’s production is incomplete without the particular non-manual. Thus, these lexical non-manuals are unlike the non-manuals required by prosody (such as the slight head nod that occurs in many citation forms) [Phonology - 2] or non-manuals that determine sentence types [Syntax - 1].