We've all been left scratching our heads wondering how our brains could have been tricked by an optical illusion we looked at. But it turns out your sense of hearing is just as susceptible to being fooled.

The McGurk effect can actually cause us to hear things differently based on what we're seeing, usually relating to the movement's of another person's lips while talking. It's an unsettling effect to experience, but nothing compared to the Shepard Tone Illusion—shown during the second half of this video—which will have you wondering if you can ever trust your ears again.