In a very deep skillet or broad saucepan, warm oil, garlic, and chile flakes over low heat; do not let garlic brown. When garlic is soft, at least 5 minutes, add crabs (keep heat low to medium low; liquid in pan should barely bubble) and cover. Meanwhile, bring a large pot of water to a boil and salt it.
Let the crabs cook until they give up all their liquid and become firm, about 15 minutes. When crabs are almost done, begin cooking pasta. When crabs are done, use tongs to remove them and hold them while cutting up with scissors. Return to pan.
Drain pasta when it is barely tender, a little short of how you'd want to eat it, reserving some cooking water. Add pasta to crabs and toss together over medium heat with pan juices and black pepper, adding some cooking water and a little more oil if necessary. (The amount of each will depend on how much more cooking the pasta needs, and how much liquid the crabs exuded.) Add parsley, taste and adjust seasoning as necessary. When pasta is perfectly cooked, serve.