it’s something we see
Watch carefully what I’m saying - it sounds like I’m saying thaw, but here’s what my mouth is really doing: except I took that audio away and replaced it with the sound of myself saying far with an F. If you close your eyes or look away, you will hear the correct sound, but if you watch, you will hear thaw because the audio and the video don’t match. Your brain comes up with some third thing that it believes true reality to be - it’s called the McGurk-a-thon, and it’s a wonderful illustration of the fact that speech isn’t just something we hear, it’s something we see.