As you might have noticed, things placed in or behind a glass of water will often look distorted or broken. This is a result of light refraction. Light moves in a single direction, but when it moves from one medium to another (like air to water), it changes directions. That means when you stick a straw in your glass of water, the part that's submerged looks like it's in a different place than the part that isn't. It also make the object seem stretched out and wide.
YouTube channel illusionphile takes advantage of this phenomenon with two videos showing what light refraction can do. The video above messes with different patterns, while the second video, below, shows how objects can disappear behind glasses of water when the conditions are just right. Take a look.
Primary image courtesy of YouTube.
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