By observing the photos and studying the thickness of the foreign body, we think that the foreign body should be a hard piece of plastic, but in our workshop, there are soft plastic bags and harder and thicker plastic sheets.By observing the photos and study the thickness of the foreign body, foreign body that we think should be a hard piece of plastic, but plastic bags in our workshop are soft and harder thicker plastic plate.By observing the photos and studying the thickness of foreign matters, we think that the foreign matters should be hard plastic sheets, but in our workshop are soft plastic bags and harder and thicker plastic plates.