My high school orchestra director once stopped a rehearsal when at least two instrumentalists in the same section played a wrong note.
"Hmmm," he said. "That must be a misprint."
He then looked at the players' scores.
"No," he said. "Misplayed."
That was the only time I remember him conveying, "Be careful and play in tune," that way. It's an effective method, provided you don't use it too often.
