The reason why the crab is traversing: The crab relies on the geomagnetic field to judge the direction. In the long years after the formation of the earth, the geomagnetic north and south poles have been reversed many times.
The reversal of the geomagnetic poles has left many creatures at a loss and even caused extinction. Crab is an ancient migratory animal with a small magnet in its inner ear that is very sensitive to geomagnetism.
Due to the reversal of the geomagnetic field, the small magnets in the crab body lost their original orientation. In order to survive in the reverse of the earth’s magnetic field, the crab adopts the practice of “changing in order to change”, simply not moving forward, nor going backwards, but walking sideways.