Shrimp is one of the most popular seafood choices around the world. It’s quick to cook, packed with flavor, and works beautifully in everything from fresh salads to pasta, stir-fries, and grilled dishes. But there’s one question that continues to spark debate in kitchens everywhere: What is that dark line running along the shrimp’s back—and should you remove it before cooking?

Many people call the dark line the shrimp’s “vein,” but that isn’t actually what it is. The line is part of the shrimp’s digestive tract, and it may contain material from what the shrimp has eaten. Depending on its contents, the line can appear light brown, dark brown, black, or barely visible. It’s usually much easier to notice in larger shrimp. Once people discover what that line actually is, the next question is almost always the same: Is it really safe to eat?