horse.rb

require 'observer'
include Observable

class Controller
  def temp(val)
    changed
    notify_observers(val)
  end
end

class Horse
  def initialize(name, maxtemp, controller)
    @name = name
    @controller = controller
    @maxtemp = maxtemp
    controller.add_observer(self)
  end
  def update(val)
    if val > @maxtemp
      puts "Fuck, #{self} has died of overheating"
      @controller.delete_observer(self)
    end
  end
end

controller = Controller.new
Horse.new(Time.now, 10, controller)
Horse.new(Time.now, 20, controller)

controller.temp(110)