Reminds me of Jeff Bridges during The Hateful Eight. Apparently Jennifer was using the real McCoy as the scene didn't involve Bridges breaking the guitar - it's not in the script, he ad-libbed [sic] it during that take. Since there was no reason to tell Bridges (or any others) about the authenticity of the guitar, no one bothered to do it; but Jennifer, who was supposed to be handling the guitar, knew, and so her reaction is genuine in the moment - that wasn't acting, that was Jennifer freaking out because she knows exactly what just happened.
Wow ... interesting factoid. I've never seen the movie though ... not a big movie guy.
EDIT: I've never seen the movie either. I'm also not a big movie guy, despite watching basically everything RedLetterMedia puts out.
This is true. It's a shame to have something that old and valuable nearly destroyed no matter who's at fault, so I agree.