[matthew321]

Whenever there is a spirit or something you always catch it with your peripheral vision but never a good look. Is there a reason for this besides the entities being fast?

I always hear people say "hey I think I just saw _______ in the corner of my eye but when I looked it was gone" There might be a reason for this. I hear all the time with ghost hunters and even just average people.

I would like to hear people's thoughts on this.

Anyway I'm not sure if that one question would be appropriate so I shall add an example. All the time when I am out side I will see odd movements in the corner of my eyes but when I look at it directly nothing is there. But then I look away an the movement is back. The movement can be anywhere from in the sky to the ground. But it is still movement and it happens too often to be animals. Especially if it can be repeated.

[LeXtruX]

that's quite normal, think about the stars you can hang on the ceiling or walls that emit ligth in the dark... the corners of ur eyes are more sensitive to light and such so we can see those thing, whereas we look straight we don't have that advantage anymore.

I have two thoughts on this,
  One. Nothing is there.
When you are looking at something, your eyes make thousands of small movements to stay in focus. That movement is amplified farther away from the focus point, which may cause a "shape" or movement in the corner of your eyes. If you combine this with Pareidolia (your mind trying to make a significant object out out random shapes, ie. face in the clouds, etc.) you "see" something.
 Two. Something is there.
If something is there it doesn't want to be seen, but like was said by Lady, you can see it better by not looking directly at it. I liken it to the pictures that you can't see the image until you stop focusing on it.

The delineation of light receptors in the back of the eye is not uniform. There are in fact concentrations or rods and cones that are standard in our species.
That is why we see the purple end of the spectrum when we do not look directly at them, because the area at the back of the retina does not have a high level of rods.
Cones are slightly to the side and are better at seeing this spectrum. Hence when we look at stars in the night sky we see them better when we look at a slight angle.

This is a sound rational explanation that satisfied me for many years.
However i now wonder if it is something a lot more mysterious than this.
Maybe i will get around to typing my new thoughts up. I am a little busy just now though.