In the 1860s Hermann von Helmholtz showed that a musical tone is not one thing but a stack of pure sine waves — a fundamental at frequency f and harmonics at 2f, 3f, 4f… The recipe of their loudnesses is what we call timbre: why a clarinet and a violin playing the same note sound nothing alike.
A clarinet's bore is a tube closed at one end, so it can only sound the odd harmonics — f, 3f, 5f… each fainter as 1/n. That missing every-other partial is exactly the recipe of a square wave, and it is what gives the clarinet its hollow, woody voice.
Silence the fundamental itself and something strange happens: leave 2f and 3f sounding and you still hear the pitch f. Your ear rebuilds the missing fundamental from the spacing of the harmonics — the same trick that lets a tiny phone speaker sound like it has bass it cannot physically produce.
Everything here is honest: the eight rods set eight real sine oscillators, summed live in your speakers and drawn on the same trace you see.
Something in the simulation stopped unexpectedly — the lesson continues without it. Nothing you did was wrong; you can move on.