Normally,when ruby is not able to find the method,it usually raises
"NoMethodError: undefined method "methodname"".That's what we always stuck,nothing special.
Above all,because of Ruby is a kind of dynamic language,what it does exactly if it can't find the method is calling "method_missing" method and method_missing raises a NameError exception,what is the point? you're able to apply the method_missing method in your application and do something cool.When we use hash,we normally call hash["key"] or hash[:key].What if we would like to call it something like hash.key.And here is a bit tricky used of it.

def method_missing( id, *args )
      if self[id].nil?
	      m = id.to_s
	      if /=$/ =~ m
		self[m.chomp!] = (args.length < 2 ? args[0] : args)
	      else
		self[m]
	      end
      else
        self[id]
      end
end
h = { "foo" => "bar",:blah => "thinkruby"}
h.blah  # => thinkruby
h.foo   # => bar

It's not bad,right?