Here we are on Planet Earth, busily pointing our radio-telescopes at the sky in the search for aliens transmissions. Hundreds of people are in therapy for alien abduction and missing time episodes which modern neurology attributes to temporal lobe epilepsy. Thousands of people have seen glowing lights which may or may not be space ships and may or may not by the 0015 flight to Heathrow, or Houston, or Charles de Gaulle. Some have seen the aliens among us - they are men in black or men in gray, they have luminous skins or gray skins with high foreheads, bald pates and large dark almond-shaped eyes. Some maintain that the US Government is covering up a crash-landed alien vessel.

In fact, millions of people live with aliens in their own homes. They live among us unnoticed. They go about their mysterious daily business unnoticed. They are small and furry and lack opposable thumbs. They are cats. Even more worrying is the fact that these small, furry, friendly aliens are Planet Earth's only defence against an alien threat which we cannot even see!

When a cat sits there in the middle of the living room floor staring into space, what is it doing? Is it pondering the mysteries of feline life or concentrating on a spider on the wall opposite it? Is it absorbing solar energy or simply sleeping? In fact it is doing none of these things. It is in touch with the mothership, an alien vessel orbiting earth at 90° to normal time and space. Information is being uploaded to the mothership. Mission details are being downloaded into the little furry alien's brain.

This mission involves ridding the earth of greeblings - the invisible extra-dimensional ancestral enemy of cats. There are a lot of misconceptions and much ignorance about greeblings. They are a scourge of modern times in their invasion of Planet Earth. They are vile creatures, fiendish and difficult to know and moreover they are invisible to humans. Those few humans who do seem greeblings are generally totally insane and no-one believes them anyway. Our alien felines have specially evolved senses allowing them to see and kill greeblings. They are our planet's last and only defence against this alien scourge which has wiped out thousands of sentient species throughout the known galaxy.

Cats allow humans to think they are cat-owners in order to infiltrate our homes and conduct counter-greebling activities which their humans dismiss as 'the crazy half hour'. So successful are cats at infiltrating our households, that when a cat dies it is almost always replaced by another cat so that anti-greebling activities continue.

Cat-owners have the most experience of greebling activity, although most have not had any direct contact with a greebling. Greeblings are believed to have invaded Planet Earth following a phenomenal population explosion on a planet in the distant galaxy Andromeda (M31). They are extra-terrestrial, extra-planar, fourth-dimension creatures and Planet Earth's only defense against them are the counter-forces of another alien species - the domestic cat - which is attempting world domination in its own, far more subtle way.

Somewhat beyond the moon's orbit, the cat mothership keeps in contact with its ground forces. Stray cats are advised of areas where greeblings have reached large concentrations. This accounts for the build up of cat colonies and also for the small tabby cat sitting on your doorstep beaming 'adopt me' signals directly into your brain. The cats' home planet was wiped out by greebling infestation, but a number of survivors escaped in spaceships. Wherever greeblings have appeared, the cats quickly follow and allow themselves to be domesticated.

A greebling's life-cycle takes place over a time scale unimaginable to humans. It is easiest to view greeblings as being a more or less constant presence, predating Earth history, and, in all likelihood, existing past our planet's inevitable end. In conventional Earth history, greeblings first built up to troublesome levels in ancient Egypt and the Indus Valley. This accounts for the supposed domestication of cats in these areas some 7000 years ago. The cats simply beamed down their ground forces into greebling hotspots and adopted human habitations as a local base of operations in the galactic battle between cat and greebling.

Greeblings arrived left their home planet after a recent evolutionary "adjustment", triggered by over-population, enabled them to go many generations without the common constraints of life as we know it. Successive waves of greeblings spread out in ever-widening spheres originating at M31. Several millenia ago, Planet Earth was has been reached by the outermost ring of migratinging greeblings.

Migrating greeblings can exist without food and water in their "pure energy form" though this is not their preferred form. The entire purpose of their outward expansion while in that form, is to discover new planets to infest. When they reach a suitable planet, they revivify in forms suitable to prevailing local conditions.

Upon revivification, the trans-evolutionary greebling colonizer is generally mistaken for the helpless young of any native animal especially rabbit young and baby birds. This is why cats hunt these creatures, knowing that they are not actually helpless young and will not grow up into cute fluffy bunnies or twittering birdies. This is the only time when greeblings might be visible to humans. The greeblings' behavior is not motivated by malice, or even conscious thought as we know it.

In their Earth-adapted form, a trans-evolutionary greebling has almost no mass though they vary in apparent size from about 1 inch to almost 20 feet across at "physical" maturity. Since greeblings intersect with our reality, they don't really have definite size or mass, they are more like diffuse electron probability clouds or a giant probability "waves". Our own physical limitations and senses mean we speak of greeblings in terms of existing at a "location" and having a "size", however greeblings exist at right angles to our own reality and merely intersect with it. All we can strictly say is that there might be a greebling, over there somewhere, and no-one knows how big it is anyway. That stirring more of dust in the kitchen might be a greebling 'seen' with peripheral vision or the greebling might occupy the entire kitchen so that we are, in effect, inside the greebling.

The most perplexing type of greebling encountered by cats is the "Bed Greebling". These attach themselves to humans in their beds, but for some inexplicable reason the Bed Greebling always expires (possibly the habitiat in the bed is inimical to greeblings). It does this with a squeaking or groaning sound (some may expire silently) and immediately explodes, releasing foul-smelling gases. These gases are highly toxic and any cat snuggled under the covers will immediately bail out of the contaminated area. Even humans, with their inability to detect greeblings, will generally fluff the covers to dissipate the noxious greebling emissions.

Greeblings spend much of their time time engaged in a feeding activity called "gravity sliding". The friction between the greebling and gravity provides sustenance. Gravity sliding is a process of controlled falling. This accounts for the fact that greeblings are often "seen" dripping from the ceiling, where they cling tenaciously, so as to prolong the final descent through the gravity field of the earth. An "engorged" greebling will then "bud off" new greeblings. As a greebling slides, the friction between itself and gravity causes an extremely high frequency "sound" beyond the normal range of human hearing. Greeblings themselves are silent. Greeblings communicate with each other and form close familial and mating bonds during certain phases of their lifecycle (the rest of the time they reproduce by budding off new greeblings). The greeblings' life-style life is notably uncomplicated in comparison to the human life-style.

No human has seen or heard a mature greebling and only a few have seen them in their revivified larval stage when they are mistaken for baby animals. Using senses beyond human understanding, our alien cats can sense the presence of greeblings with pinpoint accuracy, even recently revivified larval greeblings which are mimicking other life-forms. Experiments have ruled out any of their known senses. In fact, greeblings are detected using additional alien senses which cats evolved on their own home planet during a greebling infestation. It is speculated that cats and greeblings have co-evolved as predator and prey on an inter-stellar scale.

Although a greebling might be right in front of them, most cat owners just wonder why a cat is suddenly fascinated by a barely perceptible smut on the ceiling or why it experiences a sudden uncontrollable urge to dash, full speed ahead, from room to room in an activity appropriately nicknamed "chasing Martians". Except of course, greeblings do not come from Mars although they may have stopped of for light refreshments on the red planet before arriving on Planet Earth.

Ceiling-staring and mad, random dashes are positive indicators of greebling activity. The greeblings continuously drip from the ceilings and ooze across the floor and back up the walls. Anti-greebling manoeuvres account for other commonly observed feline activities known as hunting rug mice, hunting duvet mice and hunting toilet roll cardboard tube mice.

As well as consuming gravity friction, greeblings obtain nourishment from maintaining a proximity to a chosen human/cat family. It is possible that greeblings are studying humans since there is no real reason for them to remain confined indoors -they can exist in the dead of space or on the surface of the sun with equal ease. Once a home or apartment building (the latter allowing greeblings to "slide" from floor to floor through many storeys) has been infested, it is practically impossible for humans to get rid of them. However, cats and kittens can kill greeblings at an incredible rate. The reproductive powers of greeblings are incredible; they breed prodigiously and do not seem to fear "death" at all. Death for a greebling is akin to reincarnation for humans - merely a transfer of consciousness and a change of state.

Cats enjoy playing with, and killing, these creatures, despite the fact that in death greeblings emit horrible "noises" and an unbelievably putrid odor; described variously as "fetid socks" or "beer farts". Despite a thorough search, it is impossible to locate the source of this smell since it seeps into our reality from extra-dimensional space where the dimensions intersect.

After successfully neutralising a localised greebling threat our furry aliens will sit motionless, relaying this information back to the mothership. Their whiskers and ears may twitch as the signals are sent and mothership responses received. In return, the crew of the mothership (rumoured to be hyper-intelligent cats of the Siamese breed) send the co-ordinates of nearby greebling nests and information.

One or two cats per household is generally sufficient to balance the greeblings. In cat-free zones, the greeblings run amok, the major effect of which seems to be a subtle but profound emotional malaise known as Sick Building Syndrome. Cats are attracted to areas of high greebling density which is why some households find themselves "adopted by a cat". Some areas are more prone to greebling attack, perhaps due to localised gravity wells. In these areas, humans are gently manipulated to adopt whole squadrons of cats to neutralise greebling incursions.

Greeblings are not especially physically harmful to humans, but if allowed to build up to sufficient numbers they can cause annoying problems with household appliances, plumbing, electrical systems, car engines and computers. They are familiar to software engineers as "bugs" or "gremlins" (itself a corruption of the term "greeblings").

Greeblings have weak electrically charged fields, which may be either negatively or positively charged. This may be how greeblings determine gender, reproductive condition or even identify individual greeblings. It has been conjectured that dust bunnies are caused by the greeblings' electrical field though this hypothesis has now been rejected.

There are theories regarding the greebling's appetite for odd socks, and their habit of emitting things that closely resembles wire coat hangers and plastic carrier bags as waste products through their ability to convert energy to matter and vice versa. In fact diligent research by Harvard scientists has demonstrated that socks and ballpoint pens are larval forms of a creature which ultimately develops into a wire coat hanger after first passing through the carrier bag stage of its life-cycle.

Research conducted by agencies of various world governments over the last 50 years has amassed a large body of information about greeblings, while overlooking the presence of the furry little aliens who keept the extra-terrestrial pests at bay. However, as is typical of world governments, this research has been conducted by defense agencies and is motivated by a desire to harness the powers of the greeblings in some sort of inexhaustible power source or as weapons.

It is rumoured that the American Government has a secret Greebling Research Facility at Area 51 where they have developed methods of containment and observations of greeblings. The scientists conduct long field. This electrical field may be either positively charged or negatively charged and may play some part in their reproductive strategy or in gravity sliding. There are numerous theories about the greebling's appetite for odd socks and stray ballpoint pens, and their habit of emitting things that closely resemble wire coat hangers and plastic carrier bags as waste products through their ability to convert energy into matter and vice versa.

There is every reason to believe that parallel research conducted by agencies of various world governments have information far beyond what is generally known. as usual, it can be assumed that this research is motivated by a desire to harness the powers of the greeblings as an energy source, a weapon or possibly in the quest for instantaneous matter transport systems.