This is German singer Anne-Maria Hefele, who has filmed herself demonstrating some polyphonic overtone singing techniques, where you sing multiple notes at once.
"Overtone singing is a voice technique where one person sings two notes at the same time," Hefele explained. She's been practicing the technique for almost 10 years.
While singing, Hefele can simultaneously sustain one constant low note and also a high-pitched scale.
As io9 pointed out, it's especially cool at 3:25 when she moves the notes in opposite directions.