Auditory illusions are illusions of hearing. I recently was watching a Ted talk with this really creepy auditory illusion:
I definitely don’t believe that there is actually a Satanic message hidden in the reverse of this song. I do think that once you are told what to hear, your brain will pick out these sounds and fill in the blanks where words or sounds are missing. Humans have evolved to be pattern-seeking animals, and once we find a certain pattern it’s really hard to un-hear it.
This is an excerpt from a TED Talk that included some other really interesting pieces on things people think are real (like crop circles or a fake device used to find marijuana in students’ lockers). Here’s the full talk if you’re interested: