Remember the triumph you felt in elementary school when you figured out that the optical illusion was both a rabbit and a duck? See if you're so smug after listening to this audio illusion:
The recording is an astonishing demonstration of how your brain uses prior information to make sense of the world. The audio filter-altered sentence sounds like gobbledygook until you hear the original voice, and then your brain easily decodes the random sounds it heard before (I remember having the same sensation after hearing the Beastie Boys' "Intergalactic" a few times.) It's sort of an audio version of demonstrations like this paragraph, whose jumbled words are mostly legible due to our existing knowledge of what the words should be.
The audio illusion is part of a new exhibit at Philadelphia's Franklin Institute called Your Brain, featuring 80 interactive exhibits that demonstrate the amazing, wild ways our brains work, and somehow continue to work after being blown away by exercises like this.