Initial affricates and fricatives become final plosives. Implosive fricatives are unknown, and implosive affricates unlikely. Many languages lack a distinction between voiced and voiceless obstruents (stops, affricates, and fricatives). Basque has a distinction between laminal and apical articulation for the alveolar fricatives and affricates. Polish obstruents (stops, affricates and fricatives) are subject to voicing and devoicing in certain positions. Unlike plosives and affricates, labiodental nasals are common across languages. The opposite process happens with fricatives, affricates, laterals and trills. Manners of articulation with substantial obstruction of the airflow (stops, fricatives, affricates) are called obstruents. These affricates (especially ) have simplified into fricatives in some dialects. The strongly aspirated Khoekhoe affricates are simply aspirated plosives in Khoemana. Continuants contrast with occlusives, such as plosives, affricates and nasals. They also distinguish voiceless, voiced, and ejective affricates at each of these. Speakers are noted for their production of dark L and postalveolar affricates. This occurs with the tense fricative and all the affricates as well. Kehrein analyzes phonetic affricates as phonological stops.