Rekuhkara

Rekuhkara is a style of singing, similar to Inuit throat singing, that was practised by the Ainu until 1976 when the last practitioner died. The Sakhalin spelling or the Japanese spelling can also be encountered.
The Ainu method involved two women facing each other, with one forming a tube with her hands and chanting into the oral cavity of her partner. The technique is essentially one where the "giver" provides the voice and the "receiver", holding her glottis closed, uses her vocal tract to modulate the sound stream.
Attempts have been made to recreate the sound of this practice.