Wave your hands in front of it, first. If that doesn’t get you an answer, try to pick up a corner and peek underneath. Not all of them can be dealt with this way, many will just likely slide through your two little fingers, you’ll remember, you are alone. You’re never with a ghost. The absence isn’t there any more than anything is there, it’s just nothing with a shape. You might try walking through it. 5 to 7 chance the shiver will tell you something. Hold your hand in the cold, that’s an idea, the whispers might travel clear enough through your bones to hit your ear drums, you might hear something. Ignoring it with your back is another strategy, but your back is more sensitive, gives away more, than you think it does, and then the ghost starts learning about you, better ways to conspicuously avoid you into your most vacuous state. Then you’d be a ghost, too, and then you might understand it better. Though at that point it doesn’t matter. You’re not matter anymore. Matter grips anti-matter, never goes well, always leaves a scar.