I wrote this simple program but it won't work.  What am I doing wrong?

puts 'Welcome to McDonald\'s, can I take your order?'
order = gets.chomp

 if order == yes
  puts 'Go ahead.'
 else
  puts 'Look, I asked a simple yes or no question.'
  puts 'Yes, or no now, can I take your order?'
  order = gets.chomp
 end

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