Log Entry 130601.64

As the days pass, the crews' tensions are beginning to settle; they are not as nervy as they were. An air of normality has returned.
Even I have become accustomed the shadows or should I say shadow. When I see it now, although I still can't look at it head on, I can determine that it's not the shadow of an object. It's a single, mathematically straight column of darkness that usually saunters around the periphery of a room. I say usually, because today it was different.
I was heading towards the turbolift on my way to meet the guys in Starboard-7. We had resurrected Games Night and Starboard-7 was the logical venue. Karl loved it too as it brought more people in. Anyway, as I walked, I suddenly became aware of its presence behind me. Turning my head, just enough for it to register on the periphery of my vision, there it was. A long, tall column of shadow drifting down the centre of the corridor, fix to the floor and ceiling like a tram. It looked stronger, thicker, blacker than it had done before, and that it was in the middle and not clinging to the edges of the corridor, the way it usually did, struck me. As it approached, I stepped off to one side eager not to be touched by it. I don't care if it's not really there; it still freaks me out. The hairs on the back of my neck stand on end and I don't want to make contact with it.
In the odd way that I have developed, I looked down at my feet but kept the shadow in sight via the corner of my eye. The shadow passed me by and continued on its way, equidistant between the walls. I began to follow it when an ensign emerged from the turbolift at the end of the corridor. He was engrossed in a datapad and my heart missed a beat as I realised that he was going to walk straight into the shadow.
Turmoil filled me. Should I shout a warning? If so, a warning of what? And was there any danger if he did walk through the shadow? It was just a shadow after all.
I stood in my quandary and my mouth opened in preparation to speak although no words formed in my mouth.
The ensign, meanwhile, oblivious to the danger, suddenly deviated from his path, as though allowing someone to pass by, and then returned to his original route. Momentarily, he looked up, saw me and smiled. Then he looked behind him as though to see who else was in the corridor, who he had stepped aside for, but he saw nothing. He scratched his head in confusion, convinced that someone had been there, shrugged and then continued on his way.
So some part of him had registered the shadow, but not enough to spook him?
What is that shadow?