Please answer the following question: Extract the answer to the question from the following context. Question: What moves through grooves? Context: Towards the center, at the end of the groove, there is another wide-pitched section known as the lead-out. At the very end of this section the groove joins itself to form a complete circle, called the lock groove; when the stylus reaches this point, it circles repeatedly until lifted from the record. On some recordings (for example Sgt. Pepper's Lonely Hearts Club Band by The Beatles, Super Trouper by Abba and Atom Heart Mother by Pink Floyd), the sound continues on the lock groove, which gives a strange repeating effect. Automatic turntables rely on the position or angular velocity of the arm, as it reaches the wider spacing in the groove, to trigger a mechanism that lifts the arm off the record. Precisely because of this mechanism, most automatic turntables are incapable of playing any audio in the lock groove, since they will lift the arm before it reaches that groove.
Answer:
the arm