Young musicians often practice a difficult passage repeatedly until it sounds smooth. The improvement is real, but part of it may depend on the preceding attempt still being active in memory. A teacher therefore asks her pupils to alternate among passages with different rhythms. At first, each return is uncomfortable: the player must identify the rhythm again instead of continuing a movement already prepared. During a concert, however, a difficult entrance is rarely preceded by ten identical attempts. The performer has to recover the appropriate movement from a changing musical context. Alternating passages does not make repetition unnecessary. Rather, it changes what is repeated, from the movement alone to the act of selecting and initiating it. The teacher judges the exercise not by the smoothness of the final practice attempt but by what happens when a passage returns after an interruption.