一眼之龜
Từ Điển Thuật Ngữ Phật Học Hán Ngữ
A sea turtle with only one eye, and that underneath, entered a hollow in a floating log; the log, tossed by the waves, happened to roll over, whereupon the turtle momentarily saw the sun and moon; an illustration of the rareness of the appearance of a Buddha; also of the difficulty of being reborn as a man.