Most people dismiss this as nothing, however there is a supernatural explanation for this; Shadow People.
According to believers, they are shadow-like humanoid figures, and can only be viewed by your Peripheral vision.
They are generally believed to be evil and aggressive, although there are few who believe them to be Guardian Angels.
In the United States, Shadow People have been described as the most regularly reported paranormal phenomena.
A paranormal researcher named Heidi Hollis was interviewed several times, and she said she believes that shadow people have always existed, and that they feed
upon fear, and can be repelled by positive thinking.
There are others who believe that shadow people are
extra-dimensional inhabitants of another universe.
Below is an email regarding a personal shadow people experience in which the person caught a picture of what appears to be a shadow person.
|The picture was sent in with the email|
Both email and picture were taken from here.