beak, bill
觜 centers on the hard, pointed mouthpart of a bird: a beak or bill.
觜 combines 此 (a phonetic element) with 角 (horn), originally referring to a horn-like beak. The modern form preserves this structure.
The top 此 looks like a bird's head with a pointed beak, and the bottom 角 (horn) reinforces the hard, horn-like beak shape.
For シ, imagine a bird using its beak to sip water: sip -> シ, and the beak is the tool for sipping.