China Walls has never needed much help in the “scary” department. The notorious South Shore of Oahu surf spot, a left-hander in the Portlock neighborhood, is all shallow reef, exploding backwash, and a takeoff perilously close to the lava-rock wall. Jamie O’Brien has called it the “most dangerous surf spot on the South Shore.” On Monday afternoon, however, the danger came from somewhere else. Check out the posts here and here , from the aftermath of a shark attack, as well as below. View this post on Instagram Around 4:30 p.m., 24-year-old surfer Albert Westpfal was paddling around the reef with his college friend Zach Sheerer when a 12-plus-foot tiger shark attacked. According to Westpfal’s account posted by Honolulu Ocean Safety, the shark first slammed into his board with enough force to make him think he had hit the reef. “It was stormy surf with big short period swells smashing into the wall,” Westpfal wrote.…