Mission day three, sitting in lunar orbit, the LM docked to the CM, and this conversation happens:

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What are they talking about? "Little fluorescent circles"? "All the engineering that went into those damn things?" And what's the "big monstrosity"?

Transcript from here (onboard voice)

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    $\begingroup$ To my surprise, the annotated flight journal transcript does not have an answer (your bit starts at 079:58:49 -- 3 days 7 hours = 79 hours). They start talking about urine contamination on the LM immediately after, which could be the 'little fluorescent circles', but I've no idea what the monstrosity is. $\endgroup$ – Russell Borogove Jul 10 '19 at 21:45
  • $\begingroup$ Yeah, I did look around before posting. $\endgroup$ – Organic Marble Jul 10 '19 at 22:25
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    $\begingroup$ I love the crossed-out "CONFIDENTIAL". $\endgroup$ – DrSheldon Jul 11 '19 at 2:03
  • $\begingroup$ @RussellBorogove how would urine contamination result in little fluorescent circles? $\endgroup$ – Magic Octopus Urn Jul 12 '19 at 20:30
  • $\begingroup$ @MagicOctopusUrn Yellow crystals catching the light could conceivably be mistaken for fluorescence. It's a reach but I don't have any other ideas. $\endgroup$ – Russell Borogove Jul 12 '19 at 22:24

This seems to be a case of the "visual light flash phenomenon" described in section of the Apollo Program Summary Report:

Astronauts of Apollo 11 and subsequent lunar missions reported seeing flashes of light while relaxing in the darkened command module or while wearing light-tight eye shades. These events were generally described as colorless star-like flashes, narrow streaks of light, or diffuse light flashes. The flashes were observed during translunar coast, in lunar orbit, on the lunar surface, and during transearth coast. The frequency of occurrence of the light flashes typically averaged about one flash every 1 to 2 minutes.

I believe that Armstrong and Aldrin feared at the time that the phenomenon was caused by their spacecraft failing. That would be the references to "the engineering that went into those damn things" and "this big monstrosity". Fortunately, the spacecraft was fine, and the phenomenon was attributed to cosmic rays:

Evaluation of reports obtained from Apollo crewmen has established the reality of the phenomenon. The hypothesis generally accepted to explain the origin of the light flashes involves exposure to high-energy cosmic ray particles. One or both of the following mechanisms are suggested: (1) relativistic cosmic ray particles passing through the eye emit Cerenkov radiation that produces the light flash sensations; (2) direct interactions of high-energy cosmic ray particles or their secondaries with the retinal cells or associated optic nerve tissues produce the light flash sensations. Results of laboratory experiments during which human subjects were exposed to X-ray and several types of particulate radiation have shown that such radiation does produce similar light flash sensations, and further suggests that most of the light flashes observed by the Apollo astronauts are due to direct interactions of ionizing radiation with cells of the visual nervous system.

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    $\begingroup$ I think this has a low probability of being right. They would not think flashes in their eyes were a failure of engineering, and I can't imagine the relevance of a "big monstrosity" to those flashes. Your quotes are ok, but they don't support your thesis "that Armstrong and Aldrin feared at the time that the phenomenon was caused by their spacecraft failing." You'll need more to convince me of that. $\endgroup$ – Organic Marble Jul 11 '19 at 2:46
  • $\begingroup$ @OrganicMarble: On one hand, they talk about "engineering", "time and money", "fail", and "failure". That suggests they are thinking about something man-made failing. On the other hand, Aldrin says "No" to both the CM and LM, and the SM wouldn't be visible from either craft at that time. The incident is not mentioned in the post-flight report (first place I looked). Someone needs to ask Buzz Aldrin. $\endgroup$ – DrSheldon Jul 11 '19 at 3:03

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