You should not eat the shell of a sunflower seed. The shell, also called the hull, is tough, fibrous, and indigestible, and eating it can cause digestive issues such as intestinal blockage, constipation, or damage to the digestive tract. The kernel inside the shell is the edible and nutritious part. While eating a small accidental amount of shell is not typically harmful, intentionally consuming the shells is unsafe and not recommended, as their sharp edges could also scrape the throat or esophagus. It's best to eat shelled sunflower seeds or spit out the shell after eating the kernel.