Imagine you're conducting a high school orchestra. Your violinists have just made an inadvertently imprecise entrance, in which numerous players started playing within nanoseconds of each other. This unintended domino effect makes the entire orchestra burst out laughing. In my experience, most conductors will bring the piece to a halt and tell the offending section, "Violins, please count (or focus, or concentrate.)" Sometimes, conductors might sigh, shake their heads, or roll their eyes before telling the offending players, "Make sure you practice that section thoroughly before the concert."
There's another option, however, that I've only seen a conductor use once. During an All-State Orchestra rehearsal in which such a ragged entrance occurred, the conductor waited until everyone had finished laughing. He then did an exaggerated, deliberately enunciated imitation of our laughter.
"OH, HA, HA, HA!" he said. "HEE, HEE, HEE! HO, HO, HO!"
This had the orchestra in stitches all over again, but the conductor's unexpected reaction did the trick. Everyone relaxed, got the laughter out of their system, and nailed the entrance on the next attempt.
