《徐霞客游记·游武彝山日记》
我就顺着壁凹之处爬行，不大一会儿凹处逐渐低矮，石壁也逐渐险峻，便顺着地势弯下腰弓着背。岩壁凹处越往低越狭小，我便像蛇一般伏身贴地用膝盖爬着前进，到达壁坳转弯的地方，上下悬隔只有七寸，宽度也只有一尺五。
余即从壁坳行；已而渐低，壁渐危，则就而伛偻；愈低愈狭，则膝行蛇伏，至坳转处，上下仅悬七寸，阔止尺五。
I crawled along the indented wall and in a short time the indentation became gradually shallower while the stone wall also became more precipitous, so I bent down my waist and back following the terrain. The indentation in the stone wall became narrower and narrower as it continued, so I crawled forward on my knees like a snake with my stomach against the ground, until I reached a bend in the indentation, where the height of the space was only seven inches and the width was only one foot five.