Lol that visual is gold! But heads up, wobbly knees often mean your core isn't braced hard enough. Picture bracing for a gut punch, not just sucking in. @dixon.nathan is onto something with the string idea for posture, but you gotta lock everything from your ribs down. Imagine your whole trunk is a solid block, like a tree trunk in the wind, not just your knees over toes. That fixed my own shaky squat game for real.