SPOILER ALERT: Do not read if you have not watched “Star Trek: Discovery” episode 5, “Choose Your Pain.”

Episode five of CBS All Access’ “Star Trek: Discovery,” titled “Choose Your Pain,” was a ground breaker. Not only did it explore the first openly gay relationship in “Trek” TV history — the marriage between Anthony Rapp’s Lt. Paul Stamets and Wilson Cruz’s Dr. Hugh Calber — it also featured the franchise’s first f-bombs. In a lab scene in which Mary Wiseman’s Cdt. Sylvia Tilly explored the verbal freedom afforded Starfleet officers boldly going in a streaming show, Rapp’s Stamets echoed her enthusiasm at a scientific breakthrough.

Rapp spoke with Variety about the episode’s big and small moments, including its eerie final shot.

How does it feel to be one of the first two people to say “fuck” in a “Star Trek” episode?

It was really fun. And I feel like the way that it happened felt really true in the moment.

Were you privy to any of the discussion around saying the word and how it would be deployed?

I wasn’t privy to it. But I know that it’s one of those things that, with streaming, it does broaden the latitude to some degree. I’m glad that it was done in that way and not just somebody saying “Go fuck yourself” or something like that. It was funny and also felt very truthful. I would imagine there’s plenty of scientists who in the moment of a breakthrough might have that moment where they turn to their partner and say, “That’s f—–g amazing that we just did that.” I could be wrong. But it seemed like made a lot of sense.

You and Wilson Cruz have a number of scenes together this episode, including the one at the end where you’re brushing your teeth together, where you’re just interacting the way that married couples do, which isn’t something we’ve seen often in “Star Trek” …

Well, you have Keiko and O’Brien on “Deep Space Nine.”

Yes, that’s true. What was it like shooting those scenes?

It’s really satisfying to have writing made available that shows these different colors. I’m glad and I’m proud that our writers have approached our relationship in this manner.

Were you two the first to appear in the official Star Fleet pajamas?

Yes, that’s new. They’re very, very, very, very, very comfortable.

You broke a lot of ground in this episode.

Yes. I believe that was the first toothbrushing scene.

They were electric toothbrushes, weren’t they?

We suppose that they’re kind of like a high-end electric toothbrush that probably have some kind of laser beam or something, so you literally just have to pass them over your teeth. You don’t have to scrub. They don’t really make any noise. You don’t need toothpaste. You just clean your teeth by moving it around your mouth.

Was it surprising that Stamets didn’t push back more on the idea that the tardigrade should be taken out of service?

I don’t see Stamets as saying, “I don’t believe that this is a problem.” I see him as saying, “This is your problem. You fix it.” That’s the first response. I think Stamets has been so focused on getting the drive working that he hasn’t had time to notice that it causes the tardigrade this distress. There’s also a little bit of chagrin, as in, “Now I have to go back to the drawing board. Goddamn it, Burnham, you’re making my life more difficult.” But at the same time, as a biologist, he would never knowingly put another creature in danger. So he quickly gets on board with solving a problem. And in the scene with Saru and Calber on the bridge, Stamets has already decided that he’s going to be the one to inject himself with the DNA and make it happen — but he would never tell Hugh that, because Hugh would never allow it to happen. I think that’s a really human and interesting thing. He doesn’t tell anyone, because they wouldn’t allow it, but he has to do it because it’s the only solution.

Why is he laughing when they find him in the spore drive?

I think it’s a combination of relief and joy, and having gone on a crazy trip that is mind expanding and incredible.

Is Burnham gaining any esteem from Stamets at this point?

Yes. Burnham is proving herself to be a worthy scientific mind and collaborator and demonstrating that she is a person of honor and integrity.

The very last shot of the episode — Alex Kurtzman has already talked about the fact that there is going to be some Mirror Universe stuff this season. Was that shot a hint of things to come?

There’s a lot of interesting ripple effects of the journey that Stamets is on with alien DNA and the trip along the mycelial network. It’s a glimpse into the doors that have been opened because of that.