Watch and listen as Anna-Maria Hefele demonstrates polyphonic overtone singing, a technique where it sounds as though she’s singing two different notes at the same time.
This blew my mind a little, particularly starting around the 3:00 mark, where she actually starts to be more fluid in her singing. (via @anotherny)
Update: See also Tuvan throat singing, Inuk throat singer Tanya Tagaq (who posted a photo online of her infant daughter next to a dead seal, a “sealfie”), and many other cultures who practice overtone singing. (thx, @bmcnely, @ChrisWalks1 & james)