post_note_updated.rb

post = Post.create!

post.attributes = {
  :comments_attributes => {
    "0" => {:body =>
      Lorem::Base.new('words', 50).output.split(" ").shuffle.join(' ')
    }
  }
}
puts "Updated at: #{post.updated_at.to_f}"
sleep(5)

# post will not be touched
post.save!
puts "Updated at: #{post.updated_at.to_f}"