The penis isn’t exactly a mysterious organ. Most of it’s right out there in the open, and most guys are far from ashamed to bring it out should the right occasion arise. But macho grandstanding and fallacy (or should we say "phallusy"?) aside, there are plenty of things you probably don’t know about this important piece of the male reproductive system. Check out these interesting factoids about man’s best friend. (If you haven't already, be sure to read 10 Things You Don't Know About Vaginas too!)

They Are Breakable

Unlike many other mammals, a human penis may not include a bone, but that doesn’t mean it can’t break. Yup, it might sound like a scene from a horror movie (and for the unfortunate guy who experiences it, it probably is), but penile fracture does happen, although rarely, usually as a result of a run-in with an unyielding surface, such as a the bed, a partner’s pubic bone, or even a pillow. If the collision is hard enough, the corpora cavernosa inside the penis can tear, resulting in a large, cracking sound. If it happens, get to a hospital, quick; if left untreated, penile fractures can cause damage to the urethra, eliminating a man’s chance of ever missing the seat again.

Most Are Created Equal

Despite what you might have seen in the movies (ahem, "Boogie Nights" ...) most penises are about the same size - between three and four inches when flaccid and five to six inches when erect. That isn’t to say that there aren’t outliers, but according to condom manufacturers, only six percent of the population needs magnum-sized protection. (Which, of course, suggests that about 94 percent of guys have a tendency to lie.) (Another thing you might not know? How to put on a condom properly. Find out where you're going wrong in 9 Things You Didn't Know About Putting On a Condom.)

It Isn’t a Bone ... Or Is It?

The human penis does not include a bone, but that long-known fact had many insatiable scientists wondering just how it can become - and stay - so hard. Well, Diane Kelly, a senior research fellow at the University of Massachusetts, believes she has the answer. And it’s ... pretty weird. As it turns out, the penis is a hydrostatic skeleton, which means it has a lot in common with invertebrate organisms like worms and snails. Unpleasant imagery aside, these animals use the pressure of fluid and the action of surrounding muscles to change shape - just like a penis. But what makes a penis truly unique is its highly organized layers of collagen fibers, which are arranged at zero and 90 degrees to the length of the penis. This is what gives an erect penis its structural integrity, allowing it to stay stiff and resist bending. Kelly calls this "a really effective solution to a very basic biological problem." We think it’s just kinda cool.

Orgasm and Ejaculation Don't Always Happen Together

A lot of attention gets focused on the female orgasm, probably because it can be pretty hard work to get the job done (but, hey, someone’s gotta do it!) For men, getting the job done is always assumed to be easier. And generally, it is, but that doesn’t mean that men are always on the winning track to climax. That’s because while many men (and women) assume that ejaculation and orgasm are one and the same, they’re actually decoupled, which means that one can happen without the other. According to "The Sexual Male: Problems and Solutions," ejaculatory anhedonia is the term used to describe the condition in which men are able to ejaculate physically but do not have the accompanying feelings of release and pleasure, often as a result of illness, depression or injury. It works the other way, too; some talented guys can orgasm without ejaculating by learning to isolate a muscle in the pelvic area, and squeezing it at juuust the right time.

Surgery Doesn’t Mean Free Love

It seems like the perfect contraception: no weird hormones, devices or latex. Ever. One date with a surgeon, and then it's bareback, babyproof sex forever after. Well, sort of. In reality, most men may not be able to get down to (unprotected) business as quickly as they’d like. That’s because sperm are little warriors, and they tend to stay on guard for up to two months post-op, which means that guys need to be using protection until their doctors give them the all-clear. Vasectomy can also fail (in about 0.02 percent of cases) when sperm find another route to the vas deferens in a process called recanalization. (Find out some other things you may not know about contraception in Top 9 Contraception Misconceptions.)

No Relationship Between Flaccid Size and Erect Size

This seems counterintuitive, but apparently the size of a penis when flaccid isn’t much of a hint of what it’ll look like when it’s erect. In one study of 80 men, researchers found that while some penises grew by up to 3.5 inches when they became erect, others only take on an extra half inch. That means new fodder for locker-room bragging - because in this case what you see may not be what you ... er ... get.

Vibrators Work on the Penis Too

Vibrators are largely marketed to women, but here’s a little secret: They work on men too. In fact, the penis is the equivalent to the female clitoris. So, although sensation is less concentrated, many men can achieve orgasm with the help of a vibrator, specifically by holding it under the head of the penis.

It’s a Weapon

We know men like to think of their penises as powerful, threatening things. As it turns out, the penis is a weapon - a boomerang to be exact - or at least it resembles one. In 2007, researchers in Holland put couples into an MRI and watched them have sex. What they discovered was that the penis was actually one-third longer than it appeared (of course, men have been saying this for years!) and - at least in missionary position - is shaped like a boomerang during intercourse. No word yet on what it looks like in wheelbarrow position, but rest assured that researchers are on the case.

Most Aren’t Circumcised

According to a 2007 report by the World Health Organization , only about 30 percent of men are circumcised worldwide. But that varies according to where you live; in the United States, 80 percent of men are circumcised. There are a range of reasons why circumcision is performed, including religion, health and even aesthetics, but the medical community is largely ruling it to be cosmetic, rather than medically necessary.

Foreskin Is Handy Stuff

According to the American Academy of Pediatrics, circumcision rates have been on the decline for decades. We know that men don't strictly need their foreskin, but what many people don't know is that it can do more good out in world than it can in its owner’s Jockey shorts. Really. In fact, one infant’s discarded foreskin can grow enough skin to cover six football fields. Of course, that’s not what it’s used for; it’s grown to treat burn victims and others with serious skin injuries.

So there you have it. These are just a few interesting facts about the penis. But here’s one more: Each one’s different. So whether you’re a man or a woman, get to know the big Johnson in your life on an individual level - it’ll make for a better sex life for both you and your partner.