The toothbrush seems harmless enough in its bare-bones hygienic necessity. But in a nascent romantic relationship, a toothbrush can double as a flashlight; illuminating deeper feelings about a potential partner. It could be a promise or a threat. Starting to keep a toothbrush at another person’s home is, in most cases, a way of planting a flag and setting course for a blooming LTR.

We’re well-versed in the levels of totally bullshit chill necessary in early courting; whoever shows interest first immediately loses the upper hand, etc. However, at what point does a string of sleepovers with the same person become routine? What’s the magic number at which said bare-bones hygiene can graduate from secret need to outward practice? Setting aside all the mysticism, reserved for tricking new people into believing we’re creatures impervious to mortal imperfections and conventional habit, as adults we at some point must brush our goddamned teeth.

In a generation allegedly enamored with hooking up and being vague, introducing a toothbrush can be a way to nonverbally communicate a deeper commitment. Additionally, it suggests a monogamous element, as I can’t imagine the bandwidth crucial to keeping straight a number of toothbrushes associated with just as many people. Like family and marital psychologist Dr. Dawn McDaniel says: “You don’t want to go to someone’s house and see multiple flags planted.” Sure don’t.

Upon meeting a stone-cold fox with a killer egg sandwich game at a holiday party a while back, we got cozy quick. Since we both lived alone, that greased the tracks for repeat slumber parties. I had a tiny kitten and extra toiletries, so he got the first toothbrush since we crashed at my place so often. Without conversation—and all this before the requisite exclusivity talk—he gave me an extra to store at his apartment. I remember, while perched on his toilet peeing, looking over at my cheap Publix brand brush laying at rest on the counter and feeling giddy about the domestic comfort. It was a tender moment.

Quickly contact solution and makeup wipes joined my toothbrush’s spot at his double sink (#luxury). He, too, started keeping extra T-shirts and deodorant in a dresser drawer at mine. That grew into meeting parents, listing each other as ICE contacts, and further ingraining one another in the minute fibers of our individual lives. It felt like a natural, exciting progression tipped off by an unlikely catalyst.

“It’s a sign that you’re taking the next step,” Dr. McDaniel says.

True feelings can get buried deep under layers of apathy and the prevalence of ambiguous terms like “hanging out.” Mile-markers less tangible than the toothbrush—like the prospect of taking someone new to a favorite dive bar or introducing them to close friends—have a special magic in revealing how you really feel about the person, or the speed at which that "hanging out thing" is chugging along.

The introduction of the toothbrush shows vulnerability—whether giving one to partner or BYO(T)Bing—because it shows interest, affection, and a desire to move forward. That introduction, too, risks rejection. Even if that rebuff has less to do with actual feelings about the person tethered to the toothbrush and more about personal comfort in pacing.

A few weeks into seeing each other, my friend Meredith’s new boo said she could start leaving a toothbrush at his spot. She didn’t return the invite quick enough, apparently. “When he asked when I was going to let him bring his over, I flipped out and was like, ‘CALM DOWN. I DON’T LIKE THIS PRESSURE,’” she told me. Although Meredith’s hesitation didn’t stem from a lack of stokedness about the dude himself, it did act as a natural speed bump in the developing relationship. “I felt bad for freaking out, it was all just really soon,” she says. Taking a little space and time helped the relationship grow more slowly and carefully—possibly leading to their thus-far successful and inspiring cohabitation.

“Sometimes, it’s one of those things where it triggers feelings, where you realize you’re not ready for that or you are ready for that,” Dr. McDaniel adds.

A toothbrush can embody an infuriating truth. The real line between a creepy move and a cute one may be defined frankly by whether or not you’re actually into the person making it.

The first time Dean pulled a toothbrush from his backpack after last call and retired to my apartment, my stomach churned. We’d been seeing and sleeping with each other a bunch for about two weeks, but deep down, I wasn’t interested in anything long-term or solid with him. It wasn’t Dean’s fault, but I hated his joke tattoo and, more importantly, I was still recovering from a devastating, then-recent breakup.

My dismayed reaction to his toothbrush must have been evident since he next asked, “What? I stay over here a lot and I don’t want to be gross.” I agreed it was pretty gross to suck on an unbrushed face and, logistically, Dean lived two train lines away. Although there wasn’t so much as an insinuation of whether or not this toothbrush would stay indefinitely, its brief cameo forced our arrangement to morph from no-strings, casual sex to something of potential expectations and—oy—feelings. I cut things off quickly after that.

Even still, to some, a toothbrush isn’t an immediate symbol of commitment and is instead very literally a means of keeping cavity-free. “I always keep a travel toothbrush in my bag,” my friend Amy says, describing early days with her now-fiancé. “It kept me from embarrassing myself with morning breath when I wanted to have morning sex.” Though not personally meaningful to Amy, the conventional weight wasn’t lost. “But I didn't advertise it initially,” she continues. “Just in case it made him feel weird.”

Certainly, there’s an essential dash of grace and/or conversation before planting the toothbrush flag, though the exact science—as with its meaning or lack thereof—remains unknown.

“I think it’s up to the individuals to interpret the meaning of it... those feelings that you feel based on the toothbrush is indicative of stuff you should be thinking about and considering and analyzing,” Dr. McDaniel says. “It might be a toothbrush for one person or it might be an underwear drawer for another person to [symbolize] steps in a relationship. They make you think where you’re at.”

And, thinking ahead, assigning such weight to a toothbrush can make for more satisfying breakup rituals. After all, nothing scrubs shower grime quite like the toothbrush of a former lover.