What does this passage from Aleister Crowley's “Moonchild” mean?

Question

So I'm currently reading an obscure novel by English occultist, poet, self-appointed religious prophet, and all-round nut job Aleister Crowley called Moonchild. It's actually surprisingly good so far in my humble opinion, but there's a passage in chapter 6 which has been bugging me for a while now. One character says the following:

“Dinner was served; the Poltergeist supplied the conversation. Never before had he been so light, so genial, so anxious to assure us of our future in Summerland; but ever and anon he touched the minor chord, spoke darkly of 'proof,' and of fish! (I beg you all to bear witness that I have not degraded myself by the evident pun). [...]”

If I understand correctly, there's an obvious pun to be made somewhere in what he said, which he didn't make; however, I honestly don't see what this pun could possibly be... If anyone could tell me, it'd be greatly appreciated; like I said, it's been eating me up for quite some time now...

(By the way: I don't think any prior knowledge of anything that happens earlier in the novel is required, but in case anyone's interested, here's a link to the entire chapter in question.)

Answer 1

There are two puns at work here. One is from earlier in the chapter. Lord Anthony Bowling examines allegedly supernatural phenomena to see whether they are real or faked. He is telling his listeners about how, as part of his research, he once spent some time with a spurious medium and her husband, who claim to be vexed by a poltergeist. The husband tells Bowling that the poltergeist communicates via planchette with his wife, telling her what to expect. For example, the poltergeist says "Look out for game!" and later that night throws quail onto the dining table.

Bowling continues:

Some time later Brother Poltergeist permitted himself some allusions to fish – in the best possible taste – and I took my precautions accordingly.

"In the best possible taste" is a pun here, alluding to the fact that fish can be tasty. Since the poltergeist manifests itself by throwing things onto the dining table, the pun on "taste" gathers additional resonance.

The husband tries to convince Bowling that if the poltergeist throws fish on the dining table, it will provide proof of two supernatural phenomena: (1) The wife is really a medium, since the poltergeist communicates to her what's going to happen (2) The poltergeist is real, since fish is mysteriously thrown onto the dining table. When the husband talks about "fish" and "proof", the "obvious pun" that occurs to Bowling, which he refrains from saying out loud, is this: The proof of the fish is in the eating.

Since there has already been a pun on fish "in the best possible taste", and since "the proof of the pudding is in the eating" is a well-known proverb, the temptation to make this pun is great, and Bowling seeks acknowledgment that he was heroic in eschewing (ha!) said pun.

There's rather a heavy-handedly arch irony at work in the story Bowling tells about the husband, his fake medium of a wife, and his fake poltergeist. I can't say that the chapter struck me as "surprisingly good" enough to want to read the rest of the work, but (to continue the series of puns) de gustibus non est disputandum. I mean, I'm vegetarian, so maybe tasty fish just isn't my thing?

Edit: @Randal’Thor’s comment to the question is on point; there’s also a suggestion that the whole spiritualist setup here is distinctly fishy.