Insane Brain Surgery Dude Sings Opera With His Skull Wide Open

8/12/2015 1:38 PM PDT

This brain surgeon didn’t have to worry about playing any tunes while operating on this opera singer ... ‘cause he was putting his talented wind pipes to work the whole time.

The professional singer was diagnosed with a glioblastoma brain tumor … and while the doc had his hands on his brain the patient belted out Schubert's “Gute Nacht.”

The video sounds beautiful … but looks so disturbing.