When the conductor’s working with another section of an ensemble I’m in, this is the game I play.
Of course, first I’m following along and making sure I know my own part. I might sight read other parts or do some harmonic analysis of the piece. I will formulate questions about the music.
But above all, I play the mind reading game. I listen to the other sections and try to anticipate what the conductor will stop to work on. There are almost limitless choices of what we can choose to spend time on in rehearsal – how often can I be correct in predicting what they will choose?
Any rehearsal game for when I’m not actively making music is a way to increase my engagement in the ensemble, solve problems faster, keep distractions to a minimum, and most importantly, learn.