Don't believe your ears.
By changing the way a person looks, you can affect how you perceive their sound. In essence, by changing what you see, you change what you hear.
The phenomenon of the McGurk effect (named after the Scottish psychologist Harry McGurk) still can't be explained, despite its simplicity. Perhaps even more amazingly, even once you know what's going on it's still impossible to avoid.
While you might think of each sense as independent from the others, the McGurk phenomenon shows just how linked everything is. Sight and sound, which seem like two entirely adverse senses can definitely have an effect on each other in this case.
Professor Lawrence Rosenblum of the University of California, Riverside gave the BBC a little lesson in the McGurk effect, as you can see in the video below. If you don't believe it all, simply give it a listen with your eyes closed.