Like in bilabial articulations, the upper lip moves slightly towards the more active articulator. It aids in mounting maxillary cast on the articulator. Labial consonants are consonants in which one or both lips are the active articulator. Dr. Rudolph L. Hanau is credited with developing the Hanau articulator in the 1920s. Taps and flaps also contrast with trills, where the airstream causes the articulator to vibrate. The passive articulator is the surface on which the constriction is created. Snow then placed the bite-fork horizontally when the casts were mounted in the articulator. Kusunda consonants seem to only contrast the active articulator, not where that articulator makes contact. He is remembered as "a conciliating and an able political articulator". The first articulator of the Law as general principle was Prentice Mulford. Matthews through his poetry became "a leading articulator of the Black Consciousness philosophy". The McGurk effect can be observed when the listener is also the speaker or articulator. "Articulator" become "Loudness Contour". Phoneticians agree that the tongue is the most important speech articulator, followed by the lips.