bird's crop or craw, wine pot
嗉 centers on a bird's crop or craw, the pouch where food is stored before digestion. The wine pot sense is a rare extension, likely from the idea of a container for holding liquid.
嗉 combines 口 (mouth) with 素, which likely contributes the sound. The character is associated with the crop of a bird, a mouth-related organ.
The mouth 口 on the left and 素 on the right suggest a simple, unadorned pouch connected to the mouth: a bird's crop.
For ソ, imagine a bird's crop as a soft, simple sack: soft -> ソ, and the crop stores food softly.
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bird's crop; bird's craw