whisper, lick, taste, petty
呫 centers on quiet, close-mouthed actions: whispering softly, or tasting and licking with the mouth. The 'petty' sense likely extends from small, trivial mouth-related acts.
呫 combines 口 (mouth) with 占, which likely contributes the sound. The exact historical development is uncertain, but the structure suggests a phono-semantic compound related to mouth actions.
A mouth 口 beside 占: imagine someone leaning close to whisper a secret, or a tongue tasting something small and petty.
For チョウ, picture a tiny whisper so soft it sounds like a butterfly's wings: 蝶 (ちょう) -> チョウ, and the mouth 口 is barely moving.