If you haven’t already seen it, I recommend that you watch the excellent TED video of Michael Shermer talking about strange beliefs and the human tendency to identify patterns when there are none, before you continue with what follows. The part about auditory illusions starts around 8:50. (Shermer’s book, The Believing Brain, is one of the featured books here at OCT).
Someone has gone to a lot of trouble to make a YouTube video of Barack Obama speaking backwards. Now if you play the video without watching it, you probably will not understand what is going on. It takes the captioning to tell you what you are supposed to hear, and then your brain obliges. The Video is of Barack Obama saying “Yes we can.”