I do it sometimes because its hard to understand the person (either because of ambient noise or different speech patterns) and watching your lips helps focus on what words are being said.
hey was i stoned when i read this the first time? people mouth your words?... Dude that's messed up... Watch your lips i get but lip sync while your talking...huh?
Comment on "Does She Watch Your Lips While You Talk And "Mouth" Your Words At The Same Time?"