背刺

• 北(north)PHONETIC
• ⺼(flesh; body)RADICAL

The back is the meat on the rear side, like facing north with your back turned away from the sun.

• 朿(sharp thorn; prickle)PHONETIC
• 刂(knife (radical))RADICAL

Using a knife to stab into a sharp thorn—that is the action of piercing.