Anna Kendrick. Photo: Paul A. Hebert/Getty

Joe Swanberg’s latest movie, Drinking Buddies, features two couples: One set is played by Anna Kendrick and Jake Johnson, the other is played by Olivia Wilde and Ron Livingston. The lines are blurry between them, as Johnson and Wilde behave like lovers throughout the film, without actually acting upon it — flirting and drinking and even sleeping side by side in semi-innocent fashion — and Kendrick and Livingston go so far as to kiss. Who’s to say which form of cheating is worse? Kendrick, who is in London shooting Into the Woods, called up Vulture to chat about emotional cheating versus physical cheating, drunk acting, and her reaction to the “Cups” phenomenon.

Joe Swanberg had you guys drink real beer during the filming of Drinking Buddies. How did that affect your performance?

During a scene at the bar, they gave me fake beer, but then during a scene where I’m playing cards with Jake, they gave me real beer, and I didn’t realize it! And so every time I lost, I was pounding beer, and I didn’t realize it was real until halfway through the take. I was like, I’m super drunk right now! And so as soon as the take was over, I had to announce to everybody that I was drunk at work. I was horrified by the idea that I was going to be the next troublesome star who got drunk and started flipping over tables or whatever. I just tried to sit quietly until I sobered up.

Was this your first time being drunk on set while shooting a scene?

Oh, yeah. Yeah. It was very, very bizarre, let me tell you. I’m sure you’ve never been drunk in the middle of your job, but it is uncomfortable. For some of the movie, it was fine, and it worked in the scene, and so it was helpful for them. But I mostly found it really unnerving.

Had you ever shot a film without a script before, where you had to improv all of your scenes?

It was my first time doing anything quite like it. We did a lot of improv on End of Watch, so I kind of think of End of Watch as training wheels for Drinking Buddies, but this was the first time I had done it to this extent. And it was crazy doing it with Ron, Jake, and Olivia because all four of us were new to this specific world of improv, but also really game for it and really excited about it. So it was a perfect combination of working with people who were really good at it, but also weren’t trained professionals. It’s not like any of us had done it a zillion times, or the rest of us were left in the dust. That marriage-conversation scene with Jake is the one scene where I said to Joe, “You have to give me the words here, because I’ve never had this conversation before.” I don’t know what a believable version of it would be, how to approach this subject in a long-term relationship. Everything else, you can draw on your own experience, but that was the one time where I was like, “I need a line!” Just to get into that thinking.

How did you work out the kissing scene in the woods with Ron, and the scene where you have to tell Jake about it?

The scene in the woods we did in one take. Ron and I were both so nervous about that, because it was supposed to be awkward and unclear whether or not something was going to happen between our characters in that scene. We talked a little about it beforehand, and it was all very, “No pressure! Let’s just see what happens!” But everybody was aware that it was an important scene. Joe was like, “Cut! Great! I’m going to put that in the movie. I don’t want to do it again.” And we were both super relieved.

And after we shot the scene with Ron, I immediately almost started crying, because I felt like, “Oh my God! I have to tell my boyfriend what happened!” And I had to come up with the words, because it wasn’t a written scene! If it were another movie, you’d think, “Okay, I’ll be as honest as possible,” but someone would have written the words for me. Here, it was like I was suddenly responsible for explaining myself, explaining what I had done, and it felt so real, because I had to admit what I had done and no one was going to help me do that. When we were filming the kissing scene, I didn’t feel like I was cheating on Jake, but then the idea that I had to tell him that I had cheated was horrifying to me. I had this unbelievable sense of guilt.

Kissing Ron is one kind of cheating. But isn’t what Jake is doing with Olivia another kind of cheating, even though nothing technically happens?

I’m so glad you brought that up! [Laughs] Because actually Jake and I got into a little bit of an argument about whether or not what he was doing was better than, the same as, or worse than what I had done. And his feeling was that what I had done was worse, and I was like, [laughs] “You’ve got another think coming, if you think that flirting with this girl, and basically dating her for the entire period of time that I was away from home, just because you guys didn’t physically kiss, isn’t cheating.” I feel like that is so much more of a transgression, and we basically figured that there is just no way that he can tell me about what is going on with him and this woman he’s flirting with at work without it becoming a huge, potentially relationship-ending fight, since he knows in his heart that it’s kind of over between them. If he had admitted it to me in a way that was like, “By the way, it’s not nearly as bad as what you did,” that would start a whole other can of worms. I think it’s a very, very interesting conversation, and not a new one. I’ve been out to dinner with friends where you debate, “Is emotional cheating worse than physical cheating?” It’s a hard question.

Did all of this improv work help you prepare for Joe’s next movie, Happy Christmas? Did you feel more equipped to tackle scenes where you’re playing opposite Lena Dunham?

This was weirdly easier because my character in Happy Christmas just wants to fill up the silence, so sometimes she just puts her foot in her mouth and comes off like a real asshole. So even though I’m exploring an ugly side of things I see in myself or other people, it was easier because I could just say whatever stupid thought popped in my head. Which was terrifying, or easier. And Lena and I had met a while before, so that was helpful. She is so good at this. She is such an amazing improviser, and I think we followed her lead. She was always the one who I followed, like you know when you have a friend you grew up with, and you still kind of revert to being their sidekick? And I think that’s a little how I feel about Lena in our film, so it was easy to do that.

Are you amazed at how well “Cups” is doing?

I am bewildered. I don’t even know what to say about it. The weirdest thing to me is that it’s outpositioned artists who are out there promoting their singles, as they should be — they’re musicians! And I’ve been making movies. Like I just made this little movie in Harlem, instead of doing something to further the success of the single, and yet there it is. It makes no sense. Don’t get me wrong — it’s so cool! But it’s bizarre to me that I’m off doing something else, and it’s happening on its own. It’s so cool. But it is absolutely bewildering.

People will want to see you do something with Kendrick Lamar next.

Yeah. It’s funny that he’s having such a moment right now, because it’s definitely one of the most popular things said to me on Twitter: “Oh, you should do a mash-up with Kendrick Lamar!” There’s a picture of our faces mashed together. It’s very weird! It just goes to show you, the Internet is mostly about wasting time.