There should be room for humor in art !
Casein is a paint similar in appearance to gouache (opaque watercolor). Casein is in fact a white, tasteless, odorless protein precipitated from milk by rennin and in casein paint, it serves as the paint's binder. According to ArtLex.com, casein is the basis of cheese, and is used to make plastics, adhesives and foods, as well as paint. Artists apply casein paint to paper, as it is too inflexible for use on canvas.