The “Big Damn Movie” is Serenity that came out on DVD Tuesday.
The easter egg is the ad for ‘Fruity Oaty Bars’ that causes River (Summer Glau) to go all Buffy on a bar full of space cowboys.
You get to the easter egg from the main menu: put the cursor on Play Movie, and hit the left arrow. A bit of chrome on right hand side will light up. Press enter.
