How did the sirens sing?

....following on the Thomas Browne blog there is another question: he inserts a parable-like thought about Achilles and the Sirens in the middle of a discussion about urns and antiquities. How do you tell which is which? Benjamin says something similar about Kafka on 2 occasions; take a piece of empirical description, he says, and you'll find the Kafka stamp on it; he cites a paragraph from Eddington on the physical world and another from Metchnikoff on the canals of the Yangste. Now the latter reference follows some comments of Benjamin on the "Great Wall of China". The story is parable-like; in it Kafka doesen't list facts about canals; he sets out the myth of the Great Wall. The Eddington piece is a bit different; in imagining physical perplexity as imagined by a popularising scientist there is a similarity with Kafka's 'heaviness' that is missing in Metchnikoff.
This quality is not obviously present in Kafka's surviving risk assessment documents that he wrote as an insurance officer explaining to operatives how to avoid severing fingers at work. Maybe the answer is Benjamins's idea of the substitutability of Kafka's prose; ie don't look at each sentence for meaning but find uses for blocks of his text and then insert them where appropriate. So the choice is with the substituter; no one wants to use risk assessment material; it is already pasted on every workplace wall as Health and Safety warnings; so that leaves symbolic activities like myth making, praying, theatre etc.