 CONT: In 1955, Doc tries to read Martys thoughts with a huge device  on his head. After Marty says hes from the future, Doc starts  saying "Do you know what this means? It means that this damn thing  doesnt work at all". During his sentence, he tried to untie his  strap under his chin and its obvious hes struggling. He doesnt  finish untying it, but in the next shot the device is in mid