composition.rb

class Dog < Animal
  def pet
    dog_petter.pet
  end
  
  private
  def dog_petter
    DogPetter.new
  end
end

Dog.new.pet

weird.rb

module FuckEverythingUp
  def destroy
    exit(1)
  end
  
  def bite_the_guy
    "rawr"
  end
end

class Dog < Animal
  include FuckEverythingUp
  include BeCute
  include MunchOnStuff
end

Dog.new.destroy