Why do crabs walk sideways?
For grown-ups: the science
Crabs usually walk sideways because their side-bending legs make that direction easiest and fastest.
Most true crabs have legs whose joints are arranged and limited in ways that make lateral movement more efficient than forward movement. They can often move forward or backward somewhat, but sideways locomotion is their usual fast route.
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Transcript
Look at that crab on the sand, scooting across the beach! Why does it walk sideways?
A crab’s legs bend mostly at its sides. That shape makes sideways steps easiest.
Its legs push against the ground, one after another. The crab can zip sideways to find food or a hiding spot.
Some crabs can move a little forward or backward, too. But sideways is usually their quickest, comfiest way to go.
So crabs walk sideways because their legs are built for it. Sideways steps help them move fast!