minced meat, trifles
脞 centers on small, fragmented things: minced meat broken into tiny pieces, and by extension, trifles or insignificant details.
脞 combines the flesh radical ⺼ with 坐, which likely contributes the sound. The exact historical development is uncertain, but the structure suggests a phono-semantic compound related to meat or body parts.
The flesh radical ⺼ on the left suggests meat, and 坐 on the right looks like two people sitting over earth. Imagine them sitting around a table, mincing meat into tiny, trivial pieces.
For サ, picture a chef mincing meat while sitting on a sack of salt: sack -> サ, and the salt falls onto the minced meat.