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When mom-in-real-life Jennifer Lopez and mom-in-the-movie Cameron Diaz get together to talk about their new film, "What to Expect When You're Expecting," Wonderwall discovered that the topics aren't quite as glamorous as you might imagine: having and witnessing C-sections, the effects of "baby brain," swollen feet and spreading ribcages, pumped-up biceps and sagging prosthetic breasts.

On their real-life experiences, first- and secondhand, with childbirth:

Jennifer Lopez: "I had a C-section, but my sister gave birth six months later -- we got pregnant around the same time -- and she asked me to be in the delivery room with her, and I was, like, 'Wow!' Because I had twins and that was recommended for me to have a C-section, and there was a part of me [that] had thought, 'I didn't get to do it the way that everybody else does.' But when I saw my sister pushing that baby out, I was like, 'Maybe this was all right! Maybe this was a better out.' So that was an experience."

Cameron Diaz: "I've seen it twice. The first time I watched was my sister, who had a C-section -- my sister was like, 'I'm not going to have this baby if you're not in the room!' And I was like, 'No, you are going to have this baby no matter what!' So I was in and they were doing a C-section and she was like, 'Will you come in with me?' And I was like, 'What? What? Why didn't anybody tell me?' I was 24, and I was thinking, 'Oh, just go in there,' and there was just like blood everywhere, my sister's guts out on a platter, and the inside, all of her intestines. ... It was crazy, dude!"

Lopez: "I don't want all those details, because there was a sheet separating me from all that going on, and I didn't have to see it!"

Diaz: "I was looking at it like, 'Oh, my God!' But the vaginal delivery was crazy -- no man should ever see it! Never let a man see that. Never."

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On the usefulness of the original book, "What to Expect When You're Expecting":

Lopez: "I found the book to be so incredibly accurate while I was pregnant, and honestly, I just see why everybody has this book and why it's the first thing that you get when you find out that you're pregnant, because it just takes you through everything. It's the type of thing everybody's talked about your whole life but you know nothing about when it's happening to you. And this book helps you to not freak out. ... I even remember after reading the book, sitting in my bed with these twins -- and I had a C-section, so I was obviously in a lot of pain, and I get like this sometimes: 'No painkillers, 'cause I don't drink, I don't smoke' -- I'm like, 'No, I'm not going to take the painkillers.' (Laughs.) But I am going crazy from the pain, and I want to hold the babies but I can't, because it hurts too much. And so I have this baby nurse helping out, and I'd say to Marc at the time, 'The babies don't love me! They don't love me and they're not going to know me and they're going to love the nurse!' And I start crying and the whole thing. And he's like, 'The babies love you, trust me! They don't even know anything yet.' I'm like, 'No, I'm their mother -- I should be holding them!' And I open the book, and it was on this specific day that you get this hormone drop and it's the 10th day and it's called the baby blues, and I was like [counts on her fingers]. 'That's happening to me! That's what's happening to me right now!' And it made it so much better, because, really, you do really feel out of sorts, and you don't know what's going on. And so in that sense, it's just a great tool book."

RELATED VIDEO: Check out more interviews with the cast of "What to Expect When You're Expecting"

On Cameron changing physiques for the movie:

Diaz: "Those were my natural pistolas. It's called consistency: You have to be consistent with fitness, but what was fun about that part was that I love to work out. It's just for me, I love it, and it's something that I enjoy doing, and I think it's important to take care of your body -- not just for today but for the rest of your life. I stay fit because I want to be 60 and doing all the things I'm doing now, and so I like to stay strong. Being in one place and being able to train consistently, eat properly, do all that and then dance for a whole week, it changes your body. All those movements help to make the body a little bit tighter."

On Jennifer's brief moment of pregnancy panic:

Lopez: "I had a real ideal pregnancy. I was on tour until I was six and a half months pregnant, and I didn't really blow up until I was, like, eight and a half months -- with the nose, the whole thing, the ankles and everything -- but I wasn't really scared. I remember having one moment of panic sitting in the living room, just sitting there, and I think it just hit me that I was going to be responsible for two other human beings. And just for one second, just for like 'Boom!' -- like a wave -- and then it went away. But the realization in your subconscious is there, but then it hits you again when they start talking. Like, 'Oh my God! I have to control this somehow! You can't do this, you can't do that' But I just had a really great time, and I still am. When you have kids, every day they just bring so much joy and happiness to your life. They just bring you right back down to earth."

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On bodily changes, both real and via movie magic:

Lopez: "I used to fit into the [designer] sample sizes that only had to open up the hips a little bit for me, but up here, I was like, 'Mmm, just like the models' ... But now my ribs opened up a little, and your body does change. [My feet got bigger, too.] I was like, 'What am I going to do with all these great shoes?' But it does go back -- almost."

Diaz: "[Matthew Morrison] got to see my prosthetic breasts -- my pregnant breasts -- which were really amazing. I was like, 'Wow! Those are awesome!' But then, when they put them on, because it was just the top part in the Atlanta heat, I aged about 40 years by the end of two hours. They were literally hanging down to my hips! They were just drooping down, like they were just melting off my body, and it was really not attractive. I flashed Elizabeth Banks when I first got them, too."

On the popular notion that a woman's brain shrinks by 8 percent when she's pregnant:

Lopez: "I was on tour, the song starts and I was like [makes a blank face], 'Anybody know the lyrics to this song?' I totally forgot the lyrics to my own song! And I was like, 'This is bad,' but then I was, like, 'I'm pregnant -- who cares?' And I look back at my band and I'm like, 'Anybody?' They didn't know if I was just having a moment, and I was like, 'I really just don't know the words!' You do, you get baby brain."

Diaz: "I definitely should not have a baby then, because I ain't got 8 percent brain to spare!"