The title may allude to a line of dialogue from LD’s first episode, “Second Contact”, where Mariner says she was once trapped in a sentient cave for weeks: “You ever been trapped in a sentient cave? That’s a dark place that knows things.”

This episode consists mainly of flashbacks to unseen adventures in caves, but since these are new ones, it doesn’t qualify as a clip show like TNG: “Shades of Gray”.

The Cerritos is in orbit around the planet Grottonus. Mariner hates caves, probably due to her experience described above. Boimler remarks that caves kind of look the same, a sly reference to the reuse of cave sets in various TNG-era series.

Mariner sarcastically mentions how rocks successfully block centuries of technological process. In LD: “Mining the Mind’s Mines”, it’s said that it’s not a real day in Starfleet until comms get blocked.

Tendi talks about being trapped together (in a turbolift) right after the “rage virus” outbreak. We didn’t see them being trapped, but the rage virus incident happened in the first LD episode, “Second Contact”. Picard was trapped in a turbolift with some children in TNG: “Disaster”, and Una was trapped in a turbolift with Spock in ST: “Q and A”.

LT Steve Levy is a science officer best known for claiming that Wolf 359 was an inside job and that the Dominion War didn’t happen (LD: “No Small Parts”). Gammanite is a fictional element that Levy used to boost communications signals in a previously unseen adventure. He’s voiced by Fred Tatasciore, who also voices Shax.

This is Kyron IV’s first appearance in lore. Coincidentally, Kyron IV was the name of a character in the fantasy comic book Soul Saga by Steven Platt, the character being King of the Dominion and father to Princess Persephone. Also, a chyron is the term for an electronically generated superimposed caption (named after the Chyron corporation).

In the flashbacks, our Lower Deckers are wearing LT jg pips, which places these after LD: “Twovix”.

Vendorians are a shapeshifting race first seen in TAS: “The Survivor”. A Vendorian was last seen in LD: “Envoys” on Tulgana IV, disguised as an Andorian. Vendor Prime was seen on a star chart in PIC: “Maps and Legends”, which placed it within the territory of the Romulan Free State, in the Beta Quadrant (in LDs time that would place it within the Romulan Star Empire).

Boimler lists Levy’s conspiracy theories: Wolf 359 wasn’t real, Q doesn’t exist, Picard is a hologram and the Doctor isn’t (he also believes they are living in the Mirror Universe). Levy’s description of Vendorian brood pods and young bursting out of chests is reminiscent of Gorn breeding practices as mentioned in SNW.

Levy claims the Vendorians falsified data that going at warp speed damages subspace. If this is correct, that provides a canon explanation for why the Warp 5 limit imposed in TNG: “Force of Nature” was quickly forgotten after TNG ended. Previously, it was suggested by off-screen sources that either warp engine design was improved so as to prevent such ecological damage or that the variable geometry nacelle pylons seen in the Intrepid-class were also supposed to compensate for it.

The idea that the Vendorians are putting people through tests of character and morality is new, although such tests are usually from more powerful or omnipotent species, like the Metrons in TOS: “Arena”, the Melkotians in TOS: “Spectre of the Gun”, the Vians from TOS: “The Empath, the Q from TNG, and so on.

This is the first mention of Porgian swamp rash, although Porgs are the cute little penguin-like creatures seen in Star Wars: The Last Jedi. Also the first appearance of Balkus IX. The Star Wars reference may not be a coincidence, since the brain-eating Grafflax sounds like “Graflex” - the Graflex 2 Flash Gun was used as the basis for Anakin/Luke’s lightsaber prop in Star Wars: A New Hope and it’s still called a Graflex lightsaber in fan circles.

Thusa transferring her “base mind by dermal contact” to Rutherford is reminiscent of Spock transferring his katra to McCoy at the climax of ST II, except that this transfers their consciousness into a protein mass that creates a cloned infant version of themselves. Rapid alien-induced pregnancies are also a trope in Star Trek, most notably in TNG: “The Child” with Troi and in ENT: “Unexpected” with Trip.

The trope of an apparent monster turning out to be defending her offspring turns up in TOS: “The Devil in the Dark”.

Delta Shift were our Beta Shift Lower Deckers’ nemeses in previous seasons (LD: “Terminal Provocations”, “Room for Growth”). The ones accompanying Mariner are ENS Karavitus, ENS Asif and ENS Amadou. ENS Moxy is not present.

The shuttle that Mariner crashes is the Kings Canyon. As with all Cerritos shuttles, named after a Californian National Park. She was last seen in LD: “In the Cradle of Vexilon”.

“Dunsel” is a term used by midshipmen at Starfleet Academy to describe a part that serves no useful purpose (TOS: “The Ultimate Computer”). Rutherford used the same term in LD: “The Stars at Night”. Pergium is an element used as fuel in nuclear reactors (TOS: “The Devil in the Dark”). Amadou and Mariner pronounce it with a hard G, i.e. “PER-gi-um”, when in the original episode it was pronounced “per-JEE-um”.

As Mariner ages, she gets a grey streak through her hair like her mother, Captain Freeman.

Mariner says they’ll get T’Ana to grow Asif a new leg. She may be referring to the biosynthetic limbs used as prosthetics (DS9: “It’s Only a Paper Moon”), which use synthetic muscles in their construction.

Tend’s flashback begins right at the end of “Second Contact”, with the same dialogue from the episode, with the ship still showing damage from the rage virus outbreak.

Synthehol is indeed supposed to affect the people like alcohol, except that its intoxicating effects could be dismissed at will (TNG: “Relics”). However, starships still carried supplies of real alcoholic drinks as the taste difference was allegedly apparent to connoisseurs.

A targ is a Klingon animal, like a cross between a boar and a dog with spikes on its back, kept as pets (TNG: “Where No One Has Gone Before”).

Tendi mentions another unseen cave story where they met themselves, but they turned out to be aliens from the future pretending to be them, harkening to story elements from episodes like TNG: “Time Squared” and TNG: “Future Imperfect”.