Originally Posted by Marcie
I don't get it..
It was a play on words between 'seaweed' (the noun) and 'sea (noun) weed (verb - urinated)'. The first instance relates to the joke because you'd expect to find both seaweed and crabs on a beach. The second instance also does because it explains why the crab blushed.
It is common knowledge that irradiated cats have 18 half-lives.