This is a very cool demonstration! Make sure you only use a spoonful or two of water - I tried to do this repeatedly, but with too much water, and was getting very frustrated by the lack of results. When I broke down and followed the directions, it worked beautifully. I had to do it 3 times in a row just to marvel at it!
Place a spoonful of water onto a plate. Add a drop of food coloring and swirl to mix.
When the water has settled, add a few drops of rubbing alcohol to the center of the water.
Watch the water pull away from the alcohol - the alcohol has less surface tension than the water. The water molecules want to stick together (literally), so they pull away from the alcohol, leaving a hole in the middle.
Watch the edge of the water. It literally quivers as it tries to stick together. So cool!