speaking evil, gobbling sound made by ducks
唼 centers on a harsh, noisy mouth action: speaking evil or making the gobbling sound of ducks. Both meanings share the idea of a mouth producing unpleasant, rapid noise.
唼 combines 口 (mouth) with 妾, which likely contributes the sound. The character is associated with noisy mouth actions, but the exact historical development is uncertain.
A mouth 口 beside 妾, which looks like a person standing under a roof. Imagine someone under a roof making evil remarks or quacking like a duck.
For ショウ, picture a duck making a loud gobbling sound during a show: show -> ショウ, and the duck's noisy mouth matches the kanji's meaning.