A clear glass
Fill half a glass with water.
Add 3 teaspoons of baking soda and stir till it completely dissolves.
Add 1/4th cup of vinegar to the glass of water.
Add the raisins into the glass containing the mixture of baking soda, water and vinegar.
Observe what happens.
How does it work?
When the raisins are dropped into the glass, they begin to sink to the bottom of the glass due to their density. Since they have a rough and dented surface which is filled with air pockets, they attract carbon dioxide gas (formed due to the mixture of baking soda and vinegar), creating bubbles on the surface of the raisins. The carbon dioxide bubbles increase the volume of the raisin, without changing its mass, thereby reducing the density of the raisins and making them float to the top.
The raisins rise to the surface where the carbon dioxide bubbles pop, making the raisins sink again. The whole process is repeated, making it look as though the raisins are dancing.