In addition to removing the shell — which isn't always necessary — you may have heard of "deveining" shrimp. This entails using a knife to remove that little black line down the back of the shrimp. First off, this isn't actually a vein, but is the shrimp's digestive tract — as if that makes it any less gross.

Is it necessary to devein prawns?

The decision to devein shrimp is basically a matter of personal preference and aesthetics, not hygiene, and the vein is not harmful to the human body if eaten. If the vein is visible through the shell and meat, and if you find the digestive tract unappealing and unattractive, then it makes sense to remove it.

Is the vein in shrimp poop?

The dark line that runs down the back of the shrimp isn't really a vein. It's an intestinal track, brown or blackish in color, and is the body waste, aka poop. It is also a filter for sand or grit.