The rehearsal pianist

The pianist was adaptable. When the singer asked to try the final section more slowly, he changed pace without comment. He was patient, too, returning to the same opening bar while the chorus settled on its entry. From my chair at the back, the rehearsal sounded unfinished and repetitive. Yet each interruption had a purpose. By the third attempt, I could hear a difference that would have been impossible to describe when we first sat down.

From the passage, select two words or phrases that describe how the pianist responded to other performers.