lib/chatterbot/helpers.rb
def replace_variables(txt, original = nil)
      if ! original.nil? && txt.include?("#USER#")
        username = tweet_user(original)
        txt.gsub("#USER#", username)
      else
        txt
      end
    end
def replace_variables(txt, original = nil)
      if ! original.nil? && txt.include?("#USER#")
        username = tweet_user(original)
        txt.gsub("#USER#", username)
      else
        txt
      end
    end
do some simple variable substitution.  for now, it only handles
 replacing #USER# with the screen of the incoming tweet, but it
 could do more if needed