Perfectly melted chocolate, like in the first bowl, is smooth and creamy.
If chocolate has been melted over too high a heat or has come in contact with a small amount of liquid, it can tighten, or become seized, as seen in the second bowl.
To make seized chocolate smooth and creamy again, use a whisk to or beat in at least 1 tablespoon melted butter, vegetable oil or melted vegetable shortening. Heat over very low heat, if necessary, stirring constantly. The result will look like the third bowl.