Ice spheres and water marbles
A set of interesting and thematically linked items, I think via BoingBoing:
A scientific hoax/trick/joke: water marbles. The video shows how to mix some chemicals in a semi-complicated way; at the end of the process you can reach into a container of clear liquid and pull out the liquid in perfectly spherical solid globules.
I've seen a similar trick before, and there's a very brief moment in the video when you can see something you're not supposed to be able to see, so I didn't find this very convincing. But I can see that something like it would be a cool trick in real life.
Another video gives an explanation of the trick; that link goes to a page that sells the product that makes the trick work, so I recommend watching the first video first if you want to see if you can figure it out.
The other set of quasi-related links is a different way to turn water into solid spheres; in this case, it's not a trick, and the spheres are made of ice. To turn a lump or cube of ice into a sphere, you can use an ice-sphere machine, also known as an ice ball mold. The latter page includes a brief video of the device in action. It looks gorgeous, and the resulting spheres look nifty, but at nearly $200 for even the smallest version, I don't really need this. Still, super cool.
A much much cheaper (but also far less stylish and Victorian-tech-looking) option is the silicon ice ball maker. You fill the mold with water and then put it in the freezer. Still pretty nifty, even if not as elegant as the other approach.