His technique may not be orthodox but it's definitely efficient. I timed it and he chops an onion in, roughly, ten seconds. Which is less than what it takes to do it with a domestic food processor—considering that you have to cut the onion first, put it in the machine, close the lid, chop it, and take it out again.
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The technique appears to be very similar. Two cross cuts and then the final chop, he just doesn't half the onion first.
That has got to be one sharp damn knife though. Definitely faster than my old slap chop, and certainly easier to clean up.