crab
螃 centers on the crab as an animal. The single given meaning is straightforward and concrete.
螃 combines 虫 (insect/creature) with 旁, which likely contributes the sound. The character was created to represent a crab, a creature with a shell and legs.
The left side 虫 suggests a small creature, and the right side 旁 looks like a crab's body with legs spreading out. Picture a crab scuttling sideways.
For ホウ, imagine a crab blowing bubbles on the beach: blow -> ホウ, and the crab is making foam.
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