Abstract: The invention relates to a method for bringing about the transformation of a medium such as carbon dioxide or other gases or mixtures thereof into snow. In accordance with the invention, the aforementioned medium and the snow produced from it are caused to interact with surfaces of a snow-producing nozzle extending from a discharge orifice for the medium. The aforementioned medium, after exiting from the discharge orifice, is either permitted to expand into an elongated space which exhibits a uniform cross section. Or the medium is also permitted to act against a number of obstructions in the form of flexible bristles situated along the flow path of the medium as it flows out between the discharge orifice for the medium and an outlet for the formed snow. The produced carbon dioxide snow is intended for use in small animal pest decontamination. Means for producing snow are included in the invention.