ITP2 - OOP Tutorials - Inheritance - super

...we put the swim method in the Fish class, but some mammals can swim as
well. We don't want to move the swim method into Animal because not all
animals swim, and we don't want to create another swim method in Dog
because that violates the DRY principle. For concerns such as these,
we'd like to group them into a module and then mix in that module to the
classes that require those behaviors.