Phonemically, whistled fricatives /S Z/ are rare, limited almost enll tirely to Southern Bantu. Reports differ as to whether they are realized with labial protrusion and/or rounding. Phonetically, whistled sibilants are common; they are regarded as a feature of disordered speech in English. According to the clinical literature, unwanted whistled fricatives are triggered by dental prosthesis and/or orthodontics that alter the geometry of the incisors-not by aberrant lip rounding. Based on aeroacoustic models of various types of whistle supplemented with acoustic data from the Southern Bantu language Tshwa (S51), this paper contends that labiality is not necessary for the production of whistled fricatives.