Aliens

Aliens are a fascinating phenomena, because they're so uniquely boring. For the most part, they appear to be simple caricatures of humans. They often contain the most basic, elemental structures: the eyes and the mouth, a head separated from the trunk by a neck, and four limbs arranged for bipedal motion and freeing the hands for independent manipulation.

The idea that people are not alone in the universe is not a strange one, it's quite old. The idea that humans are the dunces of the interstellar community is not strange either. Naturally humans don't have readily available space travel of any kind, so it seems only natural that extraterrestrials would visit us, instead of vice versa. It seems only natural that aliens would develop along the same path we did. People striving to get really creative may take familiar elements and add them to humanity to create plausible aliens.

Generally, it's taken for granted that aliens are more advanced than us simply because it makes their arrival easier to explain and more dramatic to boot. However, the Earth had life on it for hundreds of millions of years without seeing intelligent life. Practically speaking, most extraterrestrials probably regarded having multiple cells as frivolity and went back to celiating in puddles of liquid oxygen or something. Less practical but more interesting, there may be planets that have no truly sapient life at all, home to an eternal Triassic age.

On the other hand, perhaps these aliens are quite intelligent, but held back by an environmental barrier. Aquatic Earth species like dolphins have proven to be intelligent, but discovering the recipe for rocket fuel would be quite a trick if your planet is waist deep in water. Or it could be that the planet never suffered a carboniferous period. Perhaps the structure of the plants and animals would be such that their biodegredation couldn't be traced or wouldn't eventually produce petroleum, or the atmosphere is unusually, dangerously explosive.

And the senses! There is a vast array of things that can be sensed, and even more varieties of organizing the way they're sensed, and even if I were to list them all it's guaranteed I haven't thought of everything. For one, we tend to call anything dealing with light "sight", and such sight obeys the same rules of sight for our eyes. Could a species be naturally sensitive to radio waves? To radiation?

Vocalizations are a big part of most species on Earth; animal ur-languages seem to appear practically out of the woodwork. As a result, aliens often speak clear English with colorful racial accents and dialects. One book I read when I was a child challenged the status quo with species that communicated partially in the manual manipulation of warts on its body. This was quite a concept, and it continues to be, because unusual forms of communication feel like they should be an alien mainstay. Why everything in the universe must communicate by way of squeezing air through meat is a mystery. Perfectly mundane animals in the world generate and manipulate electricity (humans, for example)--it wouldn't be too farfetched for species to communicate by electrifying one another, or exchanging specially developed ambient microbes, or altering the nature of their reflective skin. Scent conversations could be expected in species built to appreciate it. Even if an alien were to use sound to communicate, it needn't be attached to his respiratory and digestive system, and their method of modulating those sounds needn't be cords in the throat attached to the ol' chest billows.