I've studied Clownfolk for many years, and put together what I feel to be one of the most complete and accurate descriptions of their physiology, culture, and instinctive behaviors in existence. I'm going to share some specifics here.
* Clownfolk are not human at all, but are rather a form of reptilian hominid that has evolved alongside mankind. The natural fear and revulsion that most humans feel toward Clown kind is the result of millennia of predator/prey interaction.
* Clownfolk are evil. All of them.
* Clownfolk wear grease paint to conceal their leathery reptilian skin from their prey. It's secreted from glands in their skin much like sweat.
* In 1478 Pope Sixtus IV issued a papal Bull declaring (among other things) that it is not, in fact, taking The Lord's name in vain to say "Goddamn Clowns". It's merely being grammatically accurate.
* Being cannibalistic, Clowns often eat their own dead, and when prey is not readily available it's not uncommon for them to descend upon their injured and devour them alive.
* Clowns nutritional requirements extend beyond flesh, and actually have a need to periodically devour souls to supplement their diet. They exhibit a strong preference for human children.
* Clowns are able to extract souls from living victims and store them in latex-like vacuoles for later consumption. These vacuoles look like colorful balloons, and are lighter than air when they are full. The exact process remains a mystery.
* Clowns possess only rudimentary intelligence, somewhere between dogs and humans, but have many instinctive behaviors which have allowed them to move within human society. Common examples include juggling, animal dominance, and squeezing themselves into small spaces.
* Clowns have a crude spoken language, but only an estimated 30% (exact figure unknown) possess sufficient intelligence to form words and phrases.
* "Circus" is a Clownish word, meaning "nest" or "hive". Almost every traveling circus is, in fact, a front for a Clown raiding party. Generally humans who work with the circus are unaware of its true, diabolical nature, as there are no known historical examples of humans willingly working for Clownfolk. (There are documented cases of humans being used as slaves or kept alive in storage for later consumption, however.)
* Surprisingly, Cirque du Soleil is noteworthy in that it is the only major circus staffed entirely by human beings. Their "clowns" are humans in makeup.
* Likewise, rodeo clowns are just rednecks in costume.
* Clowns are nomadic by nature. In centuries past a troupe would move from town to town, pillaging and devouring. In modern times this behavior is largely unchanged except that it is carried out in a much more subtle manner.
* Clownfolk prefer tropical climates, but have been seen in almost every environment to which humanity has spread. The earliest evidence of modern Clown kind was discovered in Eastern Europe, but their exact origin is unclear.
* Clowns are able to enter a torpor-like state at will, allowing them to appear as statues or survive underwater for extended periods of time.
* Clown skin sheds periodically, with the old skin quickly drying out into a confetti-like substance. They also shed confetti when wounded. It's speculated that this is part of a blood clotting mechanism, as they tend to bleed little despite grievous injuries.
* Clownflesh is toxic if consumed, as is their blood. At the site of the 1821 Clown massacre in Illkirch, France, the ground was said to be steeped in blood and confetti. To this day no vegetation will grow in that soil.
* Animals instinctively shun clownflesh, though once the grease paint wears away insects and other lesser vermin seem drawn to them. Dead clowns rot very quickly.
* At least some Clown kind can produce a sticky, web-like substance. Sometimes they use it to cocoon their victims. Sometimes they sell it on paper sticks to prospective victims.
* Despite their own overpowering stench, Clowns have a keen sense of smell. It's also been speculated that they can see in the dark.
* Although there is nothing extraterrestrial about their origin, Killer Klowns From Outer Space is widely regarded as the most accurate portrayal of Clown kind in film. Stephen King's 'It' is considered a distant second.
* Clowns don't feel pain. There is a well-documented case of a squad of British Special Forces engaging a small troupe of Clown kind during the Falkland Islands war in 1982. One of the Clowns had its arm severed by automatic weapon fire, and survivors reported that it continued to fight as if unaware of the injury. There is a wealth of historical accounts to corroborate this.
* While not especially fast-moving, Clowns are extraordinarily strong. In the above case, the same clown climbed a 30' tree in less than 15 seconds with a mortally wounded soldier over its shoulder and most of a dead child hanging from its mouth. This was despite a missing arm and numerous gunshot wounds.
* It is believed that wounded or maimed Clowns have a high ability to regenerate lost or damaged tissues, though in the wild maimed Clowns are usually consumed by their own before this is possible.
* Clowns produce noxious fumes when burned, which can lead to respiratory problems- sometimes years later.
* The enlarged, red proboscis of a Clown seems to be particularly adept at smelling human fear.
* Clowns are not venomous, but like the gila monster their mouths are filled with infectious bacteria, making even a minor Clown bite a serious health risk.
* Clown reproductive mechanisms are still unknown, as are their gender differences (if any). It's doubtful that they can interbreed with humans and produce offspring, despite some evidence to the contrary (Jerry Lewis).
* Clowns lack the sophistication to use firearms, though they have been known to use melee weapons, such as bowling pins, hammers, corpses, and small automobiles.
Now you know.