Now you understand why we said mixins could give us the ability to mimic inheriting from more than one class: by mixing in traits from various modules as needed, we can add any combination of behaviors to our classes we like!
Create a module, MartialArts.
Inside, define a method called swordsman that just puts "I'm a swordsman."
On the first line inside Ninja and the first line inside Samurai, include MartialArts to mix this into both the Ninja and Samurai classes, thereby giving them the swordsman method.