Module extension within module, post class inclusion

gistfile1.rb

module FourToedFrontFeet
  def number_of_toes
    4
  end
end

module Quadruped
  include FourToedFrontFeet
  def number_of_legs
    4
  end
end

class Bear
  extend Quadruped
end

puts "#{Bear.number_of_toes * Bear.number_of_legs + 2} toes" # 18 toes

module WalksOnAllFours
  def walking_stance
    "all fours"
  end
end

module Quadruped
  include WalksOnAllFours
  def can_stand_on_two_legs?
    true
  end
end

puts Bear.can_stand_on_two_legs? # true
puts Bear.walking_stance # undefined method