Welcome to It’s Complicated, stories on the sometimes frustrating, sometimes confusing, always engrossing subject of modern relationships. (Want to share yours? Email itscomplicated@nymag.com.) Photo: J.V. Aranda

A few months into our relationship, my boyfriend and I started adding funny-sounding syllables to the beginnings of words. Hug became “higgle hug,” bed became “bibble bed,” dog became “diggle dog,” and so on, following this unspoken “iggle/ibble” rule. We once affectionately called our Airbnb host “Giggle Gary.”

I know. I’m sorry, and I know. We thought we were the only weirdos who did this, then a friend told us that he and his husband say “huggle” instead of “hug.” Couples’ invented languages may indeed be weird, but it turns out they aren’t really that unusual.

These goofy private languages take many forms, but they can be divided into a few distinct categories. Sometimes, they’re a hybrid between two people’s ways of speaking. Emily Monaco, a 31-year-old writer from the U.S. living in Paris, tells me that she and her French husband use English words with a French accent, like “tie-red” for “tired.” It’s flattery through imitation: The closer couples get, the more alike they start to speak. A 2010 University of Texas study in the Journal of Personality and Social Psychology observed this pattern in the letters of two famous historical couples: Elizabeth Barrett and Robert Browning and Ted Hughes and Sylvia Plath. Then, as the lovers were drifting apart, so did their language.

Sometimes, couples speak in plain old baby talk. Words that fall into this category tend to be full of rhymes or repeated syllables, slowly spoken, and high-pitched, says Dean Falk, professor of anthropology at Florida State University and author of Finding Our Tongues: Mothers, Infants, and the Origins of Language. They might include pet names like “Babes” or “Jolly-Wolly.” Alyssa Carroll, a 30-year-old communications consultant in L.A., has this kind of language with her boyfriend: They call string cheese “stringy dingy” and sandwiches “cinis tinis.” When we’re not saying “diggle dog,” my partner and I gross everyone out by saying “puppy wuppy.”

“It’s pretty much instinctive to talk to loved ones the way our first loves (our mothers) spoke to us,” says Falk. “The musical part of baby talk (a.k.a. ‘musical speech’) is largely a product of the right sides of our brains and conveys affect or emotion, just as music is sometimes called ‘the language of love.’”

Couples develop lexicons based not just on sound but also on significance. Some neologisms have a backstory that only the couple understands, serving as an inside joke of sorts, says psychologist and Harvard lecturer Holly Parker, author of If We’re Together, Why Do I Feel So Alone? Tania Banerjee, a 27-year-old writer in Mumbai, and her husband call babies “bandor,” which means “monkey” in Bengali and Hindi; it’s a long story, but she tells me it’s in reference to their nickname for a person they both dislike. Peter Hayes, a 28-year-old software engineer in San Francisco, and his girlfriend developed a whole language based on an internet meme describing animals as “lorge” and “smol.” Their vocabulary includes “horse” for “house,” “tort” for “treat,” and “Cross-fort” for “CrossFit.”

Regardless of the form they take, these languages help build intimacy in relationships. It seems people intuitively understand this: When a friend of mine met my partner, she told me he seemed like a keeper, in part because of our shared language. “Couples create ‘rituals of connection’ to keep their ‘culture of two’ strong, private language being one type of those rituals,” says Carol Bruess, director of family studies at the University of St. Thomas in Minnesota. “When couples have their own language rituals … they feel like they know one another in a way that others don’t, and that they have a strong connection or bond to each other. They have their own little private world.” A 1993 study by Bruess and her colleague Judy C. Pearson in the Journal of Social and Personal Relationships found that couples in happier marriages used more private language.

Private languages can also add playfulness and levity to the relationship, says Parker. They give my partner and I something to laugh about when there’s a lull in the conversation or we’re having an uneventful evening. They may even be used to point out a partner’s flaws in a lighthearted way that won’t make them defensive. “Let’s say someone has a tendency of throwing their clothes in a pile in the closet and doesn’t always hang them up,” Parker explains. “Their partner might laugh and lovingly say something like, ‘Ah, the closey-ball gnome has struck again!’”

Some private words might also make it easier for couples to talk about sex, Parker adds. For example, they might give their private parts nicknames. Or, they could reminisce on good times by resurrecting an old nickname or word.

Monaco and her partner’s use of secret words sometimes serves as a barometer of how well they’re doing. If someone uses a made-up word and the other doesn’t play along, that’s a sign that they’re in a bad mood, she explains. But the main appeal of Banerjee and her husband’s language is the entertainment it provides. “We have jokes that only we understand,” she says. “We could still crack our own jokes and have fun in boring situations.”

After knowing all of this, I don’t feel nearly as weird about saying “diggle dog” anymore. It’s a testament to me and my partner’s bond, and a way to strengthen it.

It’s also a little weird, though.