Your penis is simple: It only has a few functions, and it tells you everything you need to know about it in one glance.

The vagina, on the other hand, is a mysterious thing—an elaborate, multifaceted tool that still confounds men. And while we don’t claim to have all the answers, at least we can share these five incredible facts about her private parts.

Prepare to be enlightened and amazed.

1. The clitoris is all over the place.

That little nub you see? That’s just the tip of the iceberg. “Underneath the external glans of the clitoris is the shaft, which separates on either side of the vagina,” says Irwin Goldstein, M.D., Director of Sexual Medicine at Alvarado Hospital in San Diego. “The clitoris is actually in the range of 6 or 7 inches.”

The internal clitoris forms two “legs,” called the crua, which run along the inside of her vagina down to her sit bones.

When something moves inside of her, these legs scissor back and forth, like the motion of a nutcracker. The “nut” that sits between them is the spongy tissue of the paraurethral gland, which is where some researchers believe the G-spot is located.

So if you’re trying to hit all of her feel-good zones during sex, don’t just focus on the clitoral glans on the outside: Try propping her up on a pillow during missionary to rub against the G-spot and clitoral legs, too.

2. Women moan in the middle of the night.

About a third of women can recall orgasming in their sleep, according to a study in the Journal of Sex Research.

While nocturnal orgasms don’t happen all that often, nocturnal arousal occurs regularly during REM sleep—up to five times per night. And it’s not just her clitoris that becomes engorged with blood, but the entire genital area, making her more likely to have an orgasm.

Though your naked eyes won’t be able to detect them, it’s worth tapping her shoulder to see if she’s already primed for a midnight romp.

3. Her vagina is pH balanced.

Here’s a lesson you probably didn’t learn in your high-school chemistry class: The vagina is naturally acidic, with a pH level around 4.5. Semen, on the other hand, is basic, with a pH around 8.

This is nature’s way of neutralizing the environment in the vagina, so that your swimmers can survive in there. But having too much sex—we’re talking marathon ejaculations—can actually upset the pH level in her vagina, potentially leading to infections like bacterial vaginosis.

We’d never tell you to refrain from going all night, but make sure to let her pee in between sessions, so she can reduce her chance of getting an infection.

4. Her wetness depends on the time of the month.

When we talk about arousal, we talk about women “getting wet.” And that’s essentially right: Vaginal lubrication is one of the first signs of vasocongetion, or the rush of blood from arousal.

But her wetness can also be influenced by where she is on her monthly cycle.

When she’s ovulating, she’s more likely to have a wet, slippery fluid inside of her vagina. This is basically a cervical mucus that’s secreted throughout her cycle. Her discharge has nothing to do with how horny she is, though, so sometimes she might feel super wet without being in the mood at all.

By the way: The vagina doesn’t have any lubrication glands, so what you’re feeling when she’s turned on is actually plasma escaping from the capillaries in the lining of her vaginal walls.

“If you were to stare at the vagina during the arousal state, you’d see little droplets. Kind of like what you’d see from condensation on a cold glass during the summer,” says Dr. Goldstein.

5. Women get erections, too.

When you become hard, it’s because your corpus cavernosa—the twin tubes of erectile tissue in your penis—are engorged with blood.

The clitoris also has a pair of corpus cavernosa inside of it, which means she, too, gets erect when she’s aroused. An erect clitoris will swell, become more sensitive, and increase in size. The inside of her vagina will also expand as blood flow increases.

“The vagina has a series of accordion-like folds called rugae that, during arousal, allow the vagina to increase in length to roughly the same size as the penis,” says Dr. Goldstein.

It’s harder to see, but her body is responding to arousal similarly to your erection, although it might take her longer than it takes you. Still, it’s worth waiting until she’s totally aroused and erect. Imagine having sex with a half-flaccid penis—sound like fun? We didn’t think so.