Talking out of the side of your mouth

Talking out of the side of your mouth

This means one is lying, right? Or something else?

It means trying to keep a heated or private conversation private in a place where there's a risk that it may be heard, as Robusto suggested. Check this out: http://www.youtube.com/watch?v=cUKJWsnAAXs&feature=related&t=1m03s (one minute and 3 seconds).

I know that "talk out of both sides of your mouth" is a particular idiom used to explain the act of saying different things to different people about the same subject, so I have always associated this expression with the synonym "lying"...