Painting on glass is a popular Polish form of folk art by which the artist paints a picture on the reverse side of a glass surface.
In many parts of Poland, boys dressed in traditional costumes, one of them as a devil, another as an angel and a third as the grim reaper go at Christmas time from house to house around their village or neighborhood with a big szopka and sing Polish carols.  In exchange for the caroling and entertainment they provide, the children receive a few coins or, even better, some tasty holiday treats from their hosts.