The Feynman Way

This video's starting point is solid: Weitzberg & Lundberg (2002, American Journal of Respiratory and Critical Care Medicine) measured a 15-fold rise in nasal nitric oxide during humming versus quiet exhalation in 10 healthy subjects (from 189 to 2818 nl/min), replicated by Maniscalco et al. around the same time — it's one of the best-established numbers in this whole batch of posts. But the original study's authors themselves say the therapeutic benefit of that nitric-oxide rise 'should be investigated' — in other words, they measured the mechanism, not a health outcome. The video goes much further, linking that mechanism to vagus-nerve activation and to cerebrospinal-fluid clearance driven by breathing: that last phenomenon is a genuine line of neuroscience research, but the idea that 60 seconds of humming produces a measurable effect on that system has no directly cited source demonstrating it — the video itself files this under an 'evidence calibration' chapter, which is honest framing, but the title and edit sell a firmer causal chain than what's actually shown. Verdict: mixed — the nitric-oxide mechanism is solid and well cited, the full causal chain through to 'brain cleanup' is not.