We are used to optical illusions but less familiar with auditory illusions - yet it is entirely possible to fool the brain about what it is hearing.
Watch the video once and see what the person is saying. Then replay the video, but this time close your eyes as soon as you click the start button.
You should hear a different set of sounds the second time. This is the actual soundtrack, but when your eyes are open, the mouth shapes tell you that a different sound is being heard, and your brain overrides the sound it receives to match what is seen.
Click the image to watch the video.
Thanks to Professor Arnt Maasø of the University of Oslo who produced this McGurk effect video.