gistfile1.rb

module IncludeMe
  def included_innit
    Child.innit
  end
end

module Mod
  class Child
    def self.innit
      puts "I'm Mod's child, innit"
    end
  end

  class Sibling
    include IncludeMe

    def innit
      Child.innit
    end
  end
end

sibling = Mod::Sibling.new
sibling.innit # => "I'm Mod's child, innit"
sibling.included_innit # => exception