Real guitar and violin strings vibrate hundreds of times a second — far too fast to see. This giant loft string is slowed down 48× so you can watch every wiggle; the note you hear is that measured wiggle speed, sped back up.
Two things make the wiggle faster: a shorter string (pinch it), or a tighter string (turn the peg). Faster wiggle = higher pitch.
Pinch at exactly half the string and it wiggles exactly twice as fast — the same note, one step higher. Musicians call that an octave.
The tuner needle shows your measured note; the dashed gold tick is what the physics predicts (c / 2L). When they line up, your ear and the maths agree.
Something in the simulation stopped unexpectedly — the lesson continues without it. You can move on; nothing you did was wrong.