That being the Stormtrooper hitting his head. Just because it's a signature of the Star Wars franchise. So much so that Jango Fett hits his head in AOTC. But it certainly won't take away from all the other great work you have listed here.
Yeah, I knew that one wouldn't go down well with everyone... but hey, it was a goof until the SE, when they added a minor sound effect. And the sound effect they added to the DVD is just ridiculous.
DE