It's a miracle !
Yma Sumac - Peruvian opera singer and actress , who had worldwide fame , owned the unique voice and ability to sing in two voices .
She did not receive music education and did not know the score , she herself said she learned to sing by imitating the voices of birds
http://yma-sumac.com/
http://www.youtube.com/watch?v=UZ82P61Lt_c