I was at a friend's house a few weeks ago and her husband made slusies for us by just putting soda in the freezer. I had some soda that had lost most of its carbonation so I made slushies with it. I didn't have as much room in my freezer so I just put some in a water bottle. Every half hour or so I went in a shook it. After about 2 hours it was a delicious slushie.