用英文写的神秘故事,简单点的初二的100词以内

Last night,I went to a park with my friend David.After walking for some time,we were tired and sat down under a tree.Suddenly,I saw something passing by but I didn't know what it was.I asked David if he also saw that thing.He told me that he didn't see that.I was frightened.I wanted to leave and asked David to go with me.But David was still tired and he wanted to have a rest for some five minutes.I decided to wait for him.Suddenly,I saw that again.I shouted and screamed.I was so afraid of that.David was also shocked because he also saw that.Can anyone tell me what was that thing?

请给具体要求。什么样的故事叫神秘故事？