Dry ice is not ice, but a solid of carbon dioxide. It doesn't contain any water and can't be counted as snow, so it's not ice. The cylinder in the magician's hand contains carbon dioxide compressed into liquid. When the magician opens the valve of the cylinder, the pressure in the cylinder suddenly drops, and the carbon dioxide liquid will vaporize. Because the liquid needs to absorb a lot of heat when it vaporizes, the ambient temperature suddenly drops, and some carbon dioxide gas condenses into solids. Its appearance is exactly the same as snow, and it is also white, so many people mistakenly think it is snowflake.