squat
踆 centers on the physical action of squatting, lowering the body by bending the legs while keeping the feet on the ground.
踆 combines 足 (foot) with 夋, which likely contributes the sound. The exact historical development of 夋 is uncertain, but the character as a whole is associated with squatting.
The left side 足 means foot, and the right side 夋 looks like a person bending down. Picture someone squatting with their feet flat on the ground.
For シュン, imagine squatting down quickly with a 'shun' sound: shun -> シュン, as you lower yourself smoothly.