gouge, hollow out, bore, pry
抉 centers on forcefully removing material from inside something: gouging, hollowing out, boring a hole, or prying something loose.
抉 combines 扌 (hand) with 夬, which likely contributes the sound and may relate to the idea of separating or removing. The exact historical development of 夬 is uncertain.
The hand radical 扌 beside 夬 suggests a hand using a tool to gouge or hollow out material. Picture a hand gripping a chisel and prying out a chunk of wood.
For ケツ, imagine gouging out a hole and finding a ketchup packet inside: ketchup -> ケツ, and the hand pries it out.