Scott/Emmeline
That's [...] pretty terrifying. I can't recall them acting any differently. I really hope we're not looking at a Invasion of the Body Snatchers plot here.
Ah. We do have people in our world that can use it, but unfortunately it's not a very common practice. The only person in our world that I know that can do it is Albus Dumbledore. There was a rumour that VoldYouYou-Know-Who was skilled, but it's not something we're trained for.