Everyone knows about Superman's ability to blow ice breath. Anyone who's seen Superman IV remembers the scene where a single strand of Superman's hair holds up a half-ton weight. And more than comic nerds have heard about the legendary "Man of Steel, Woman of Kleenex" conundrum, which posits if Superman has sex with Lois Lane, his super-semen would shoot right through her uterus.
The point is, everything about Superman is super, including all his bodily secretions and his bodily functions. In fact, they're probably not just super, like his eyes' ability to see through things; they probably give him specific powers, too... like the fact his X-ray eyes also provides heat vision. Gross as they might be, we're taking a look to see what other powers the Man of Steel's Kryptonian body might yield — both reasonable, given how a body actually works, and unreasonable, since those are the powers Superman more likely has.
Sailva is primarily used to lubricate the mouth and help begin the process of breaking down food, including swallowing. By giving loose food particles something to get swept away by, it also helps protect teeth. It goes without question that Superman could spit so fast and hard that the saliva itself would effectively be a bullet, but that's not ever going to be Superman's style. Since spit is technically a lubricant, it stands to reason that Superman's saliva could grease any machine, perhaps for eternity. It's possible that his spit is the key to a perpetual motion machine. If nothing else, he should be able to hock a loogie at a bad guy's feet and make him fall down.
But: As mentioned above, simply having super-saliva probably isn't enough for Superman; his spit needs to grant him some other, more useful but completely ridiculous power, too. If you factor in saliva's viscosity, there are other ways it could used — sure, he'd have to have the ability to change his spit from lubricating to semi-adhesive, but that's small potatoes for Superman. Imagine Supes on top of a bridge, dangling a loogie down to victims on the ground below. Shouldn't a civilian be able to climb that strand of saliva up to safety (or, more likely, merely hold on while Superman sucks it back in)? Couldn't he use it to tie up some of his less super-strong foes? Frankly, I see absolutely no reason why Superman — or any of his less squeamish friends — couldn't go webslinging around Metropolis on the Man of Steel's super-loogies.
Crying is both a human response to sadness and a mechanism to dislodge particles from the eye before they cause damage. Since Superman has cried plenty of times during his 80-plus-year tenure in comics, we know that sadness effects him, although since bullets actually bounce off his iris, the unwanted particle thing probably isn't much of a problem. We know Superman has the capacity to hold a greate deal of liquid — he's sucked up pools, lakes and even rivers a few times, only to spit them out later — which means I say he can cry a river. Literally. Show him a picture of a dead puppy and let him go end draught forever.
But: It's tough to discover an even slightly reasonable power that Superman's crying might bestow, because the only thing you can really alter about tears is their volume. However, in the spirit of the heat rays his eyes can shoot for no goddamned reason, I'm betting Superman's tears are the panacea — the medicine that heals all wounds. It's the kind of power he'd have right this instant if DC had thought of it in the ‘50s. You know I'm right.
The explanation for Superman's freezing breath — and I was as surprised to find out someone at DC had bothered to come up with one as you likely are — is that Superman's lung capillaries are so strong that can create enough pressure to turn the carbon dioxide in Superman's exhalation to freezing temperatures. If his lungs are that powerful, then there should be no question that a Super-cough would not be pleasant for those nearby. Generally, a loud human cough is approximately the same decibel level as loud TV. So extrapolate that to Superman, and you get a cough that should create a sonic boom that knocks people off their feet and blasts objects away from him. Think Hulk's patented sonic clap, only ruder.
But: A sonic boom cough makes too much sense, and Superman does not copy the Hulk — the Hulk copies him. So I say Superman's cough rebuilds things. You have a destroyed building? Superman coughs and the pieces fly about in just such a way that the building is restored again. Has the dam busted and there's water racing towards the town? Cough! Was a priceless painting slashed by a vandal? Cough! Did someone relaunch you in all-blue with electricity powers? Cough.
This is actually one of Superman's bodily functions we have evidence for! See, when a regular human sneezes, he/she expels up to 40,000 droplets of snot at over 100mph. So what would you expect if Superman's sneezed? Work as a powerful shotgun blast? Cover his opponents with sticky but unbreakable piles of snot? Knock over nearby structures? Nope.
HE DESTROYED A GODDAMN SOLAR SYSTEM.
This is an actual panel from Action Comics #273, in which Mr. Mxyzptlk drops a ton of sneezing powder on all of Metropolis, and Superman has to leave our entire goddamn dimension and find another dimension with no one living in it to sneeze in. WHICH ANNIHILATED AN ENTIRE SUN AND ALL OF ITS PLANETS. Healing tears seem pretty reasonable now, don't they?
But: No buts. The man sneezed and destroyed a goddamn universe. There's absolutely no use handing him a Kleenex. Oh, and in case you're wondering why this is on a list of powers Superman doesn't know he has, I guarantee to you in the new 52 he's forgotten this little event (and because it's completely awesome).
Vomiting isn't pleasant, but it is a necessary bodily function, so I think we all need to be prepared for the day Superman blows chunks. Vomiting is, according to Wikipedia, "the forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose," either because you ate/drank something bad, or because you're sick. Now, trying to find out the velocity and volume of the average barf section via the Internet was taking me to some very dark places, so let's just agree Superman would put Regan from The Exorcist and her fire hose of pea-green nastiness to shame, shall we?
But: Vomiting's power is unquestionable, but it is also gross. So how to turn it not only into something useful, but more Superman-appropriate? Obviously, there's only one answer. When Superman eats bad fish, HE SHOOTS GODZILLA'S ENERGY BEAM FROM HIS MOUTH. Case closed. He makes the noise and everything.
Superman stands for Truth, Justice, and the American Way (or at least he does most of the time). Founding Father Benjamin Franklin was a big proponent of farting. I don't really know where I'm going with this, but farting is the body's way to expunging intestinal gas. Shockingly, Guinness is behind on all the farting world records other than longest, but I think we can all agree the windspeed of a human fart is negligible, and the decibels never range more than 80, about the same as a dial tone (farts generally seem louder because they're socially taboo). So Superman's fart isn't going to beat his cough in terms of the power of its loudness... which leaves the odor. Most realistically, Superman's super-farts should smell super-awful, and have the same effect as, say, tear gas on anyone unfortunate enough to smell them, incapacitating them if it doesn't render them completely unconscious. It's likely useful when he's tied up by Darkseid or something.