Bjork is incredibly overt. Read how she pretends not to know how to be interviewed (from MSNBC):
LORRAINE ALI: I have to admit when I first listened to "Medulla," I didn't notice it was instrument-free. There's so much going on—from guttural bass noises to choral arrangements—it's hard to tell it's pure a cappella.
BJORK: Is this my turn to speak? I'm just learning this new game, where you review and I answer. So now it's my turn?
B:Here I go then. I think I'll take your comment as a compliment. It's good you don't feel anything is missing. You shouldn't be listening to just a great idea, you should be listening to music. A lot of the bottom end—like the bass and drums—is just these crazy guys who make insane noises. It's the wonders of the human voice at the end of the day.
Apparently the record is made up mostly of voices, including "Rahzel the human beat box, an Inuit throat singer and Gregorian chanters." Sounds real weird.