Sin

If pepper is sprinkled on the water, it remains on the surface. If liquid soap is added, it is pushed to the edge, further added pepper sinks.

A piece of copper turns black when it glows in the flame. If the hot black piece of copper is immersed in alcohol, it becomes copper-colored again.

Sin means missing the mark: because of sin, people fail to fulfill their purpose. This can be illustrated to our children with a drawing.