Egg yolk may appear runny and uniform, but on the nanoscale, it is one of the most crowded biological fluids in nature. Packed with proteins and fats, it serves as a dense storage reservoir for a developing embryo. Yet the tiny particles responsible for transporting these nutrients—low-density lipoproteins (LDLs)—must remain mobile enough to reach their destinations. How they navigate this complex "nanoscale traffic jam" has long puzzled scientists.