in the video at 0:07
Also this part of the scene was in the non extended version. I just couldn't find a quality version of the non extended scene on youtube.
I've always wondered if this movement was meant to be a part of the shot or if they just completely overlooked the fact that one of dead uruk-hai gets up slightly to watch what's happening.
On a side note viggo mortensen parrying a real dagger, wasn't supposed to be part of the scene either. Although this is kind of commonly known I just put this in for the people who don't know how of a badass that Viggo Mortensen is.
At 4:16 in this video: