Cleaning out a live crustacean's intestines before cooking

I once read a novel (computer-crime thriller, forget the title) set in New Orleans. In one scene one of the characters shows another his pre-cooking preparation method for crayfish: He puts the live mudbugs in a collander, sets them in the sink, and then douses them with cold water with lots of salt. This forces them to empty their bowels. They can now be cooked, and they’ll come out without all that disgusting green stuff at the tail end.

Is this necessary, and would it work? (I always thought the green stuff was part of the creature’s nervous system, or something.)

Would the same treatment be necessry/effective when cooking a lobster?

I’ve conducted many a crawfish boil and never heard of this technique. If the intestine thing on a crawfish bugs you, it’s super easy to remove. When you breack the tail off a cooked mudbag and extract the tail meat, there’s a little flap that stick out the top of the tail where it connected to the thorax. If you peal that flap off, the intestine comes with it and you get what looks like a perfectly butterflied piece of tail meat. That’s how it comes if you order ettouffe in a good place.

Some lobsters and crawfish have roe in them. We call this “mustard” and it’s good stuff. No reason to get rid of it.

Lobsters for some reason that I’m not aware of generally don’t have a problem with a big dorsal intestine/vein/whatever filled with black stuff, though shrimp and crawfish do, so it doesn’t seem necessay.