This one is something I've actually done. I was having breakfast at a restaurant with my father one day, and I noticed those little plastic containers of cream they like to give you for your coffee. That got me thinking. Butter is produced by churning the milk until the fat in the milk congeals into lumps. Those lumps are butter. I looked at the creamers. Nah, I thought. Couldn't be enough fat. But! My curiosity was piqued, and I felt it bore testing. So I took one of the creamers, still sealed, and started shaking it. This agitation should cause the lumps to form. It took a lot of shaking. I think I shook it for fifteen minutes straight, as fast as I could. After what seemed like an appropriate duration, I opened the creamer. There, lining the inside, were little white lumps of butter. Amazing! It can make for a neat party trick, but it's a little slow.