Are you a fan of Prawns? Prepare them yourself, maybe? Have you ever seen a long dark part on the back of a raw prawn?
Brace yourselves…
It's their poo. And if you don't cut it out, it's not all that good for you.

Really, it makes sense. Machines can't clean a prawn that well. And prawns are generally swept up by indiscriminate nets. They don't have all that time to finish doing their “business” before their lives are ended rather impersonally.

Luckily, maybe only one out of five or so prawns have this in them. But if you're working with king-sized prawns, it's very easy to simply cut that part of the prawn out without even touching it. Getting shelled prawns also helps.
You can just about see a large black line on the prawn in the picture above. Gross!