@Ana1234 - See, this is why this is a little bit of junk science. There's no real depth to this theory. They always trot it out in magazines and things like that to fill out articles like "ten ways to know he's into you" but there are hardly ever decent studies to back up the findings.
I'm not saying there isn't truth to it, because it's almost certainly true that people will change their way of speaking and their body language depending on who they are talking to.
I mean, the way I talk to a preschooler and the way I talk to my best friend are going to be completely different.
But to what extent is that unconscious? Is it learned behavior? Does it extend across cultures? If this was a rigorous scientific theory, it would be able to at least ask those questions, rather than just hand waving them away.