Side-elevation of the same aeroelastic sway mechanic as the 3D scene: the deck, hangers and main cable oscillate together as a low-frequency sine wave under crosswind loading, the way real suspension decks (Tacoma Narrows, 1940) can flutter in strong wind. Vertical bounce = heave; the deck's slight rotation = torsional twist. Wind strength and sway frequency drive both; traffic keeps streaming across regardless.