cat.rb

module Entity
  class World
    def initialize
      cat = Entity::Animal::Cat.new
      cat.cat_method
    end
  end
end

module Entity
  module Animal
    class TestThing
      def initialize
        cat = Cat.new
        cat.cat_method
      end
    end
  end
end

module Entity
  module Animal
    class Cat
      def cat_method
      end
    end
  end
end