putrid carcass
骴 centers on a decaying body: a putrid carcass, specifically one where the flesh has rotted away leaving the bones.
骴 combines 骨 (bone) with 此, which likely contributes a phonetic element. The character specifically refers to a rotting carcass where bones are exposed.
The left side 骨 means bone, and the right side 此 looks like a stopped foot, suggesting something that has come to a halt and is now just bones. Picture a carcass so decayed that only the bones remain, stopped in its tracks.
For シ, imagine the sheen of white bones in a putrid carcass: sheen -> シ, and the bones gleam amidst the decay.