What song is this???

Recently i found a special type of song, <忐忑>
this song is the most special song that i ever heard....
you can remember well the whole song by just listen the 1st time...
but u surely cant sing the song even u heard it many many times.....

quite amaze by the performance~~~

the link is given below >>>>
http://www.youtube.com/watch?v=PuiLZHxYr78