centipede
蝍 centers on a specific many-legged creature: a centipede. The meaning is narrow and concrete, with no clear abstract extensions.
蝍 combines 虫 (insect) with 即, which likely contributes the sound. The character is used specifically for centipede.
The insect radical 虫 on the left pairs with 即 on the right. Picture a long, segmented insect with many legs—a centipede—crawling quickly, its body resembling the strokes of 即.
For ソク, imagine a centipede scurrying into a sock: sock -> ソク, and the centipede disappears inside.
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