Video from stevespanglerscience
This video demonstrates the seemingly magical effects of light refraction. As light travels from one substance to another, its speed can change depending on the indices of refraction of the two substances. If the two substances have different indexes of refraction, the light will bend as it passes through the second substance. In this video, the Pyrex stirrer seems to disappear because it has an almost identical index of refraction to the oil. The light passing through the stirring rod barely bends and makes the rod appear invisible.
To learn more about reflection and refraction, click here.