pig, hog, pig radical (no. 152)
豕 centers on the pig or hog as an animal. The radical sense is the same pig shape used as a component in other characters.
豕 is a pictograph of a pig, with the modern form preserving a stylized head, body, legs, and tail.
The top horizontal stroke suggests the pig's head, the curved strokes its body and legs, and the final sweeping stroke its tail. Put together, 豕 is a pig.
For シ, imagine a pig sitting in a field of sheaves (シ): sheaves -> シ, and the pig is resting among them.
—