It could have been a bubble, but it looks as though it came from the hole. Possibly a mishap with whatever was used to keep the hole open. Using vegetative matter around which to form the paste would prevent this, but who knows in this specific example.

My reference to 're-firing' was not to suggest that the bead has been repaired after the original firing, but that it was definitely one of those beads that was a 'problem child' for the beadmaker. She looked at this after the initial firing, muttered something choice in her native tongue, and tried to salvage her work - No guarantees, but I've been there, and it's mighty likely.

On worries from wear: They were made to be worn, no? They are some of the most beautiful beads I've ever seen, and when people see them and are interested, it's a great tale to tell about where they come from and how they're made. We don't frequent too many mosh pits, and Kim absolutely treasures this piece, so not really.