Grew up in Western New York and called it the same thing ("Mumbly-peg"). Though our version was where you simply drop the knife between your feet and then move

Grew up in Western New York and called it the same thing ("Mumbly-peg"). Though our version was where you simply drop the knife between your feet and then move one foot inward until touches the knife, then repeat until you chicken out. Looks like Wikipedia contains a similar variation: https://en.wikipedia.org/wiki/Mumblety-peg https://en.wikipedia.org/wiki/Mumblety-peg.