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With no qualifier, dumbbell snatch implies one-arm.
Place the feet at shoulder width and let the dumbbell hang at arm's length between the knees. Keep the back set and weight spread evenly on the feet. Extend the legs and hips powerfully, and pull your body back down into a squat as you continue the dumbbell's upward motion with the arm, catching with a locked elbow. The upward movement of the dumbbell should be generated with the hips and legs, not with the arm.