I noticed it a long time ago when I first wrote what became these videos, but that was on VHS I think. I was surprised at how much clearer it was on Blu-Ray. It's only a handful of frames, but much more visible than single frame I caught on video. It's hard to tell if it's been shot or is ducking for cover to the right of the corridor.
And not for the first time have marvelled at the amount of detail Cameron went into - and then found a less-than-one-second continuity error when Hudson and Vasquez test the guns.