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This is more or less the method I always used, which is called BTV (or VTO). Nothing to do with Frenzel, and you do NOT need to pinch the nose.I think of it as being a kind of yawn: where the back of the throat is opened and the muscles around the back of the jaw are tensioned. Whilst yawning, you can stifle the need to open your mouth.
And I just learned something new, thank you! I have been performing MO ;-)Problem with Frenzel is that it requires to remove the mouthpiece, as a true Frenzel can only be performed with the mouth clused and pushing up with the tongue against the soft palate.
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Most scuba divers who think to being using Frenzel are in reality using Marcante-Odaglia as they perform it with the mouth open, keeping the mouthpiece in it.