On "How I Met Your Mother," Lily calls Marshall "Marshmallow." I have been called a little owl, a swan and even a "panda-fish." No, I'm not a supernatural, shape-shifting creature or a character in a children's storybook.

I've just been in a few relationships where cutesy, affectionate nicknames emerged as inside jokes.

These names stuck around for months, even years – to the point where hearing "Elizabeth" or "Liz" in certain contexts would suggest a truly serious situation, or that I was in trouble.

With Valentine's Day around the corner, I got to thinking about terms of endearment and about the world of interpersonal language that romantic partners develop just for themselves. I began to wonder: Is there any science behind using pet names? Is it a mark of a healthy relationship, or unhealthy? Are couples who give each other names, ranging from the generic "Honey" and "Sweetie" to the creative "Loopy Lop," more likely to stay together? And in our digital age, are these nicknames any more important?

A quick search of the literature reveals just how little these issues have been studied scientifically. The evidence that's out there is largely based on a smattering of surveys, which didn't capture an entirely representative sample of forms of love. It doesn’t seem like anyone has made any distinctions between heterosexual and homosexual couples with regard to the use of pet names—perhaps it's not relevant?—or compared how pet names are used in the United States versus other countries. But from what has been studied, and from the experience of several experts, it seems nicknames can be a good thing for a relationship – if both partners are into it.

What are pet names good for?

Plenty of my friends have developed nicknames with their romantic partners.

I asked the question on Facebook and got a broad assortment of answers: There's a husband and wife called “Nerk(le) and (Milk)Dud," a dating couple called "Sweefy and Darsh," and former boyfriends who knew each other as "Tiger and Teddy." An American man who dated a Chinese woman told me he called her "Popo,"which means "wife" or "broken broken," depending on your intonation — and she called him "Benben," which he says means something like "dumb dumb," referring to his lackluster mastery of the Chinese language at the time.

There seem to be a variety of languages with pet names, too. According to the website of the popular language-learning software Rosetta Stone, the French say "Mon Petit Chou" (my little cabbage or cream puff), the Russians say "Vishenka" (cherry), the Dutch call girlfriends "Dropje" (candy) and in Brazil you can say "Meu Chuchu," where "chuchu" is a vegetable. In Spain I heard the term "Media Naranja," meaning half-orange, suggesting that the romantic partners are two halves of the whole. The BBC did its own international roundup 2013, which dug up terms like "Chang Noi" (little elephant) in Thai, "Ghazal" (gazelle) in Arabic and several inventive examples from readers.

But if you scour in the scientific literature for research on pet names and relationship happiness, you'll likely come upon one stand-out paper: ""Sweet Pea and "Pussy Cat': An Examination of Idiom Use and Marital Satisfaction Over the Life Cycle," which appeared in the Journal of Social and Personal Relationships in 1993. Carol J. Bruess led this study for her master's thesis, and she's still getting inquiries about it 22 years later.

"I fell in love with the idea that I could look at the micromoments that create relationships," says Bruess, now director of family studies at the University of St. Thomas in St. Paul, Minnesota.

Bruess approaches pet names anthropologically. To her, a relationship is a "mini-culture" unto itself, reinforced by rituals such as nicknames and other private language. The terms of endearment are important when conflicts arise, she says, allowing a natural recourse to humor and playfulness when things get rough.

"I think it's a really human, natural behavior to take language and shape it for our own purposes," she says. "I think that's how nicknames evolve. We name things, we give things symbols, and over time we tend to naturally manipulate those symbols toward a certain outcome."

Bruess' study, co-authored by retired professor Judy C. Pearson, specifically looked at the relationship between nicknames and the satisfaction of married people. The authors used the term "idiosyncratic communication" to talk about nicknames, expressions of affection and other sorts of "insider" language used only within a specific relationship. Bruess and Pearson found that idiosyncratic communication is associated with marital satisfaction and couples in their first five years of marriage without children reported using the most idioms.

But rather than these private words and phrases dying off over time, Bruess thinks that they become so ingrained in a relationship that long-term married couples may stop recognizing them as special. "It's become part of the fabric of their relationship," she said. "It's taken for granted."

For this study students at Ohio University went out and delivered the survey to married people. All told, 154 completed surveys came back to the researchers, and they used those to divide people into categories of how long they had been married and whether or not they had children. Interestingly, the study did not use data from couples married for more than five years who had no children (there were only two examples). It also didn't look at non-married couples. So, while this study established a basis for looking at the question, it used a small sample size and didn't represent the full spectrum of romantic relationships.

Still, Bruess believes the main finding — that idiosyncratic communication, including cute nicknames, relates to marital satisfaction — is absolutely true today.

"If we can't laugh at ourselves and with each other in the relationship, we're less likely to sustain that relationship in a positive way over time," she says.

What is normal?

I wondered if anyone had done a broader survey of the nicknames issue. Pepper Schwartz, professor of sociology at the University of Washington in Seattle, co-authored a book called The Normal Bar that collected data from almost 100,000 participants through an online survey about all things related to relationship happiness, including nicknames.

The authors gathered responses several countries—including Canada, England, France, Italy, Spain, Hungary, Australia, New Zealand, the Philippines, and China—but only analyzed the U.S. data on nicknames, Schwartz says.

The authors found that about two-thirds of U.S. respondents said they used pet names in their relationships, and that among people who said they were in "very happy" relationships, 76 percent reported using pet names. That sounds like a high correlation, too, but gives me pause as a science writer because the survey did not use randomized sampling to find participants. (A controlled study would seem a bit inauthentic, however: Assigning some couples to use nicknames, and others not to, and then seeing who's happier after a few years.)

Nonetheless, Schwartz says she thinks pet names are important as shorthand for admiration and affection. Especially for those who feel they don't get enough affection, using pet names makes up a lack of "hearing from their partner enough good stuff about how wonderful they are," Schwartz says. "It may be easier for someone to say "Hey babe, you look great' than "I love you.'"

Sex expert Ian Kerner, author of the "Good In Bed" series of guidebooks, agrees that the use of pet names is "a great thing" as long as both partners are comfortable with the names.

"Names like honey, baby, babe, sweetheart (etc.) connote a special intimacy that's reserved for your significant other," he wrote in an e-mail. "Most couples tell me they're shocked or know something is wrong in the relationship when a partner actually calls them by their actual name and not their nickname."

You may be familiar with another group of nicknames that are reserved only for certain people: families. My parents have their own nicknames for me and my brother, and we have names for them too that we don't use in public. The names have resulted in a few awkward car rides with friends over the years, but otherwise I do see it as a largely positive extension of the bonds between us.

Helen Fisher, a biological anthropologist at Rutgers University and my go-to person for all things connected to "the science of love," thinks the process of giving a sweetheart a special name may be related to how parents and children give each other pet names, too. "It's just a human way of expressing love," she says.

Baby talk

Fisher directed me to researchers at The Kinsey Institute at Indiana University who did a study on "baby talk," or what they call "Loverese," among couples. This refers to the way that people change their voices, often using a higher pitch, when speaking to a romantic partner (or baby). This is relevant because it's another example of the special speech unique to particular couples.

The Kinsey study, which has not yet been published, had about 500 participants, all in relationships, and found that, on average, couples spend 10 minutes of every hour with each other using romantic baby talk. But this speech is negatively related to relationship length, so couples that have been together for years use it less. Participants in this study did represent a variety of age groups (18 to more than 60 years old), and study authors did not control for sexual orientation or marital status.

"Overwhelmingly, people say romantic baby talk should only be used in committed relationships. That tends to be the only relationship people said that they do use this in," says Amanda Gesselman, postdoctoral research fellow at The Kinsey Institute.

"Using baby talk seems to be a way to strengthen an emotional bond between relationship partners, which is something you would want to do with a partner you want to commit to, but probably not with partners that you don't wish to be attached to," she added.

Previous studies showed that romantic baby talk is found among speakers of many languages, according to Gesselman.

"It appears to be a normal, healthy thing for couples who are very into each other, and satisfied and passionate toward each other," she says. "When it starts to taper off, people tend to be less satisfied. It doesn't mean that being satisfied stops the baby talk (or vice versa). They both seem to be declining together."

Not for everyone

Gesselman acknowledges that while her study looked at the average among couples, there could be individual differences unaccounted for. There could be couples for which nicknames and baby talk just don't work.

One expert I spoke with advises against pet names, or at least "Honey" specifically. Maggie Arana wrote a book with Julienne Davis called Stop Calling Him Honey…and Start Having Sex! in which they argue that pet names contribute to "roommate syndrome"—when a relationship goes from being sexual to one of chaste friendship.

The book is based on the authors' personal experience and on anecdotal stories from a variety of couples, most of whom they reached through friends or friends of friends. It's a small sample, but Arana stands by the general trend it presents.

"The pet names don't necessarily kill your sex life but they definitely hurt it," she says.

According to Arana, couples can improve their sex lives by dropping pet names, and she's seen many examples of this. Just being called by your own name is special, too. "We're all ego-driven. We like hearing our names. When you don't call your spouse ever by his or her name, I think you can run into trouble," she says, adding that silly names and baby talk can put people in a non-sexy mindset. "If you're calling each other Muffin, for example, it's really hard to go from Muffin to having sex."

Others say the effect of pet names depends on the individual relationship – that if both partners like it, there's no problem. Bruess in particular cautions against judging a couple based on their pet names, which emerge and exist in their own unique relationship. Again, it's like looking at a culture from the outside.

"What might be disgusting or not sexy to us might have a whole host of meanings that serves that couple's relationship well," Bruess said.

There's also the embarrassment factor, of course, if one person lets the nickname slip in front of others (I have been chided for accidentally doing this too loudly on occasion). This is especially bad if you have a pet name that would sound infantilizing or downright ridiculous to others. Kerner himself admits that he doesn't like when his wife calls him "Peanut" or "Little Peanut."

"It infuriates me if she ever accidentally calls me that in public," he says.

Here's another can of wordy worms that pet names open: issues of gender and power. Women may often take on the names of tasty objects (such as "Muffin") while men assume more macho monikers (such as "Big Daddy Rabbit"), Bruess said. Even calling someone "baby" can suggest that the person is inferior to you.

"We would hope (pet names) are there to build intimacy and not to reinforce gender power dynamics. That's probably the slight dark side of something that's otherwise fun and cute," says Justin Garcia of The Kinsey Institute, who collaborated with Gesselman on the study of romantic baby talk.

Embracing pet names in the digital age

In the digital age, when hardly anything is private anymore, couples may value their pet names all the more. Bruess, who is about to come out with a book about families and social media, hypothesizes that couples savor the privacy of their nicknames and idioms even more today because so many other aspects of their lives have become public.

Kerner agrees. "With increasingly public lives, an intimate nickname between partners is all the more important for distinguishing the false intimacy of social media from the real intimacy of direct human relationships," he says.

Whether they sound to others like gibberish or the names of Muppets, it doesn't matter. I will embrace the nicknames given to me as long as they hold positive meaning, and I'll invoke boyfriend-pet-names to reinforce emotional connection, make questions sound sweeter and break the ice when things are tense. When there's nothing left to say, at least there's that.

Even Arana, after writing a book advising against silly pet names, isn't totally immune to terms of endearment from her romantic partner.

"So you guys don't have nicknames for each other?" I asked Arana and her fiancée, Joe.

"No," said Joe, shaking his head.

"Well, every once in a while, you call me “gorgeous,'" she told him. "I don't mind "gorgeous.'"