A cel is a slide of the actual animation, these are then typically bought and sold at fairly high prices, some of them can sell in the thousands if they are real original cels of master animation pieces and popular scenes. I’m guessing this one can be had as an original for a few thousand hong kong. The cel is the work that is then used to overlay, at 24-30 frames per second, that means you get 30 very similar looking frames per second shot. You can overlay various Cels on top of each other to create background, scenery and frontend…so this Cel is infact transparent.