scoop out, gouge
刔 centers on removing material by cutting or digging: scooping out or gouging a hollow.
刔 combines 夬 (likely a phonetic component) with 刂 (knife), suggesting cutting or scooping with a blade. The exact historical development is uncertain.
The left side 夬 looks like a hand holding a tool, and the right side 刂 is a knife. Imagine using a knife to scoop out or gouge a hollow in wood.
For ケツ, picture a sharp knife cutting into a hard surface with a sudden 'kets' sound: kets -> ケツ, as you gouge out a piece.