bleached bones
骼 centers on bleached bones, specifically the dry, whitened remains after flesh has decayed.
骼 combines 骨 (bone) with 各, which likely contributes the sound. The exact historical development is uncertain, but the character is associated with dry bones.
The left side 骨 means bone. The right side 各 looks like a person sitting cross-legged. Imagine a skeleton sitting in that position, its bones bleached white by the sun.
For カク, picture a bleached bone cracking under pressure: the sound 'crack' cues カク, and the bone is dry and brittle.
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