https://www.exploratorium.edu/snacks/disappearing-glass-rods

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the above video demonstrates the optical illusion created when a piece of glass is put into a liquid with a similar refraction index as the glass.  The glass bends the light rays in a similar fashion as the water does causing the glass rods to “disappear” in the liquid.  The lines behind the tank of liquid shows that the glass of the box has a different index causing the stripes on the back wall to look distorted or “refracted” because it bends the light differently because of its index.