Two additional, and much rarer, percussive articulations are represented by symbols in the extIPA chart. Their exclusion from the main IPA chart is an indication that they do not seem to occur as typical forms of adult speech in any part of the world, although they may have some communicative function. The symbol, [ʬ], is used to transcribe a bilabial percussive sound, which might be described in lay terms as lip-smacking.