In many of the languages that contains bilabial trill, it only occurs as part of a prenasalised bilabial stop with trilled release, [mbʙ]. This developed historically from a prenasalized stop before a relatively high back vowel, such as [mbu]. In such instances, these sounds are usually still limited to the environment of a following [u].
There is also voiceless alveolar bilabially trilled affricate ([t̪͡ʙ̥], sometimes "tᵖ"), which is not often used. It is found in Pirahã and from a few words in the Chapacuran languages Wari’ and Oro Win. The sound also appears as an allophone of the labialized voiceless alveolar plosive/tʷ/ of Abkhaz and Ubykh, but in those languages it is more often realised by a doubly articulated stop [t͡p]. In the Chapacuran languages, [tʙ̥] is reported almost exclusively before rounded vowels such as [o] and [y].
Its behavior is trill. It means that we produce this sound by directing air over the articulator so that it vibrates. In most instances, it is only found as the trilled release of a prenasalized stop.
