Harmonics

Harmonics are bell-like chiming tones. A natural harmonic often stands in angle brackets <12> or as "N.H." — the string is only touched at certain frets (5, 7, 12), not fretted. P.H. (pinch / artificial harmonic) means: on the pick, the thumb grazes the string and squeezes out a high overtone. Both sound clearly different from a normal note — that explains many "how does he make that whistle?" moments.