This 12-minute video shows professional opera singer Ambroz Bajec-Lapajne singing Franz Schubert's Gute Nacht while he undergoes brain surgery.
It is common for craniotomy patients to be kept awake so they can speak or perform other high-level functions while surgeons work on them, giving the doctors a better map to work with in removing the tumour.
For Bajec-Lapajne, doctors wanted to monitor his ability to recognise changes in key, something he relies heavily on as an opera singer. By using those functions doctors the surgeons are better able to avoid harming them in the process of removing the tumour.
The most interesting part of the video takes place around 2 minutes 40, when Bajec-Lapajne's words begin to slur and his singing slows. But this, apparently, was the point of the exercise - showing surgeons where not to go during the tumour removal.
In the YouTube video description, Bajec-Lapajne writes that it has been over a year since the surgery and he is doing fine, continuing his professional singing career.