Why does quicksand trap people?

Answer: The sand-water mixture thickens when disturbed, gripping your limbs

The sand-water mixture thickens when disturbed, gripping your limbs ✓ — Correct! Quicksand is sand saturated with water, and it behaves like a non-Newtonian fluid. When you step on it, your weight and movements disturb the mixture, causing it to thicken (shear thickening). This makes it difficult to pull your limbs out quickly. The more you struggle, the more the sand grains pack together, increasing the grip. You won't sink completely because your body is less dense than the quicksand, but escaping requires slow, deliberate movements to allow the mixture to liquefy again.

The sand acts like a thick liquid that pulls you down — Wrong. Quicksand doesn't actively pull you down; it's not like a whirlpool. The danger is that when you struggle, the sand-water mixture thickens and makes it hard to move. If you stay still, you'll float because your density is lower than quicksand's.

The sand hardens and locks your feet in place — Wrong. Quicksand doesn't harden into a solid; it remains a fluid mixture. The trapping effect comes from the increased viscosity when disturbed, not from the sand becoming solid.