method_transplant.rb

module Human
  def hello
    p 'Hello'
  end
end

class Cat
  include Human

  def mew
    p 'moeeew'
  end
end

class Dog
  def bark
    p 'waaaaf'
  end

  define_method :hello, Human.instance_method(:hello)
  #define_method :hello, Cat.instance_method(:hello)
end

Dog.new.hello
#=> 'Hello'