The tongue finds the suction straw before the patient decides to let it: something in the geometry of a wet muscle and a slightly-too-strong vacuum makes contact almost involuntary, and the sound changes the instant it happens, a flat trilling whistle collapsing into a wetter, louder gulp that anyone who has sat in the chair recognizes by ear alone. The straw is the one dental instrument regularly entrusted to an amateur mid-procedure: propped in the corner of the mouth, angled toward the cheek, left to hum on its own low frequency while hands more qualified work elsewhere. Its plastic sleeve is discarded after each patient; the rigid housing underneath is autoclaved and returned to service, so the specific whistle in any given office is a fixed acoustic signature, the same pitch, chair after chair, year after year, regardless of who is holding it.
Assistants develop a preference for holding it themselves rather than handing it over, on the theory that a trained grip keeps the tone even and the mouth dry; patients who are handed the straw tend to either underuse it, letting saliva pool, or clamp down out of nervous habit, cutting the hum into short stuttering bursts. No manufacturer publishes a decibel rating for the thing, and no one has ever requested one. It remains the loudest sound most people hear with their mouth open and their eyes closed, and the pitch belongs to the office rather than to the patient, who will meet a different one at the next practice and think nothing of it.