Unknown monster

Raly and Charlottes were best friend. Every day they both like to walk together. Raly and Charlottes decided to walk to the long lake. It was really far from where they live but both of them don't mind. As they kept on walking sky kept on getting darker and darker. After an hour walking there both of them started to get tired. So they lie down and looking up in the sky. But suddenly Raly saw something behind the bushes. She turned round and told Charlottes what she saw. Charlottes turned and saw it changing shape. They both ran really really fast back to their houses. Charlottes said to her parents that "Then as I turned round it changed shape". So Raly and Charlottes parents said to not go to that lake ever again.