One day you found yourself above a huge forest, the treetops weren't far below.... Thinking... Suddenly! Ohh my God! is this the end of my life? Your senses tell you that something big is behind your back and about to set in a forceful way. You can't turn, you are too scared. Probably, move at full speed and throbbing in 20 meters distance. However, you take a deep breath and turn around. Suddenly, there is no one. What was it? What scared you so much?