Pulled my beef roast out of the slow cooker and saw these weird white stringy things poking out of the meat. They look like little worms or parasites. Is the meat infested?

Those pale, stringy pieces that appear in slow-cooked  beef are almost always just normal parts of the meat itself.  Beef roasts are full of collagen-rich connective tissue that holds the muscle fibers together. When exposed to low, slow heat, that collagen breaks down, softens, and can show up as white, thread-like strands or gelatinous bits between the fibers. It may look unsettling, but in a properly cooked roast, it’s simply a sign that the tough tissue has melted into tenderness and flavor.