How Star Wars Pulled Off BB-8's Funniest Moment

I have seen Star Wars: The Force Awakens many, many times. Every time that I have, there are two scenes that have always caused an audible reaction from the audience. First, the audience cheers, or gasps, when they see the Millennium Falcon the first time. Secondly, the audience breaks out in a fit of laughter every time BB-8 gives his "thumbs up" to Finn via a lighter he has stowed inside his body. It turns out that moment was not part of the original plan, and creating it was actually a lot of...