It was mumbly-peg in our childhood, probably contracted from mumblety-peg from an earlier mumble-the-peg.
But the game mumble-peg seems to have disappeared from the American scene entirely.
We don’t know why, unless it may be that mothers are more fearful lest their young roughnecks cut themselves with a sharp knife.
The name derives from the manner in which the game was played in England from the early seventeenth century and as brought by boys thence to America.
From various positions, toe, knee, elbow, fingers, each player in turn flipped his opened knife with sufficient force to stick in the ground.
If unsuccessful, the other players had the privilege of driving a peg into the ground with an agreed number of blows struck with the handles of their knives, a peg which the loser was then supposed to withdraw with his teeth.
Our memory may be faulty, but we doubt that after one game of mumblypeg any knife was then sharp enough to produce serious injury.