Dark soliton is a general phynomenon in broad physics subjects. In higher dimensions, dark soliton exhibits instable except one special kind as vortex. The fundamental instability of a single dark soliton in two dimensions is to eventually decay into a number of quantized vortics through what is called the snake instability. The problem is that: what the snake instability exactly means? Someone say when the soliton in one dimension going to second dimension, due to the phase change, the dark soliton will be bend, if the curvature is large enough, the dark soliton will be split into vortex-antivortex pair. I don't know how phase change plays a role?