Look closely and you’ll see that some of them do! But in general, they are concentrating deeply, just like outfielders waiting for the fly ball or pitchers winding up to a curveball. They’re “in the zone.” Some musicians “feel” the music and move in their chairs or move their heads. After the music is over, you may see them smiling broadly. If it was a concerto, and they liked the soloist’s performance, they won’t just smile – the string players will tap their stands with their bows as a sign of appreciation and others will stomp their feet.