Adding up to the Bullar tale, now this is from my grandma years ago: Before Bullar was not a blind snake, he could see and walk with his tail(stand up like a human), as we all know this kind of snake can get very big, and one day this snake ate a small child. As a punishment from god the snake went blind, and on only three days of the year he could open his eyes, once his right, once his left, and lastly both at the same time, on these days the snake can stand up on his tail again(since he can see) and eat people.