William. Ariake Sea has a lot of crabs. Like, over a hundred, as my son as a tot would have said. It occurred to me to Google why they walk sideways, and this is what I got: “Because crabs have stiff, jointed legs, they move faster and easier walking sideways. Walking sideways means that one leg never moves into the path of another. So a crab is also less likely to trip over its feet.” So now we know.