I'm talking to someone. We're in an indoors place, apparently a large hall. The place is shadowy, but not scary. We're talking normally, when I spot something strange a few meters away, behind the person. Looking over his/her shoulder, I see a spirit materialize, then disappear moments later. I'm worried about it, as apparently there was something strange about it (I mean, other than the fact that it was a spirit). Still, I pretend there was nothing wrong, and the other(s) don't seem to notice any change on my behavior. It was better if I took care of this myself, or at least didn't make them worry.