Severus doesn't actually notice the pun, so Q is safe. "Of course; try again, using the assessment charms afterwards, until you believe you've done it right four times in a row, and then show me that you reliably can. However, you'll do that practice on your own. For now, continue for ten minutes--I'll check your grip at five--while I take care of the next stage here," he gestures to the simmering cauldron, "and then we'll move on. Release the knife and pick it up again, holding it correctly."