Why Does The Eye Ball Jump?

The term eye ball jumped can be used to describe the phenomenon in which somebody is very surprised when he looks at something which is amazing. It is a phenomenon that is in use since ancient times in the country of China and mostly goldsmiths used it a lot. When they showed some jewellery to a customer they just looked at his eyes and the reaction of the eye was the deciding factor to decide the price of the jewellery. If the customer liked it the goldsmith could feel that by looking in his eyes and then quote a bigger price.
      
So the eye balls of a person jump only when he finds something which is interesting or amazing or sometimes something to fear about.