Mysterious Shadow: significant or a lot of bother over nothing?

[img]http://www.dark-torch.com/imagenes/prometheus01_mini.jpg[/img] Is it just me or do the rest of you see also that in the "road" clip (above), the top-left-hand side is artificially darkened? I appreciate that the whole thing is probably CGI anyway, but this darker patch seems unnatural. Could it be deliberate editing to hide something (as far as the trailer is concerned)? Or could it in fact be the shadow cast by a larger airborne ship? Maybe that's what the group of vehicles are retreating from (assuming they are retreating at all).