Cannot Understand LittleBookOfRuby Example

The following example is from Little Book of Ruby in Chapter 9 and is
in the file modules4.rb:

# Ruby Sample program from www.sapphiresteel.com / www.bitwisemag.com

module MagicThing
  def m_power
    return @power
  end

  def m_power=(aPower)
    @m_power=aPower
  end
end

module Treasure
  attr_accessor :value
  attr_accessor :insurance_cost
end

class Weapon
  attr_accessor :deadliness
  attr_accessor :power
end

class Sword < Weapon
  include Treasure
  include MagicThing

  attr_accessor :name
end

s = Sword.new
s.name = "Excalibur"
s.deadliness = 10
s.power = 20
s.m_power = "Glows when Orcs Appear"

puts(s.name)
puts(s.deadliness)
puts(s.power)
puts(s.m_power)

When run, it produced the following output:

ruby modules4.rb

Excalibur
10
20
20

Exit code: 0

I had expected it to produce the following output:

ruby modules4.rb

Excalibur
10
20
Glows when Orcs Appear

Exit code: 0

I do not understand why it is behaving the way it is behaving. Can
someone help me figure out why? I know that this is a Rails only
forum, but I don't know of any other place to post my questions to. If
someone can point me to Ruby forum, I would gladly to to it.

Thanks in advance.
Bharat