I’ve learned about an interessting illusion called McGurk effect. It shows how your brain is not only using your ears to hear things, but also your eyes. Sounds crazy, but it’s really like this. A specific example of the McGurk effect is hearing “da da da” with eyes opened and watching the video, but hearing “ba ba ba” once you close your eyes.
This effect is caused by playing the sound “ba ba ba”, but showing the video for “ga ga ga”. You brain will see the lip moments and decide that the only possible thing to hear is “da da da”. People who can’t lip read at all will hear “ba ba ba” and hearing impaired will hear “ga ga ga”. You won’t encounter this effect in real life, because lips are always synchronized with the voice, but in some amateur dubbed movies, the is the possiblity of you hearing something which has not been said.
I’ve found a video on Youtube showing this effect:
Here is another with an complete sentence as example: