First of all, however, let me put on a disclaimer. These factoids are not supposed to be scholarly articles. All errors are mine, however, I would appreciate it if people do not use the information that I would be presenting here as sources to their term papers. Blogs aren't really a reliable source. Cite something else, and it better not be Wikipedia!
Anyway, the world's languages have a large variation with regard to the types of sounds that people use. Some languages have a sound system that has about 25-40 sounds, although there are languages that utilize more, or less extreme. For example, Rotokas just have about 11 sounds, if I am not mistaken, and the Khoisan language !Xu has about 140 sounds all in all. And in case you are wondering, English has a larger than average sound inventory, due to the rather large amount of fricatives that English has.
Let's talk about vowels. If you have a language that only has three vowels, what would those vowels be? Most of the time, it would be /i/, /a/, and /u/. And if the language has a five vowel system, it would be /i/, /e/, /a/, /o/, and /u/. Anybody can think of why that is the case?
So why is it that this is the case, and not that a language would have /i/, /e/, and /æ/ instead?
This has something to do with perception. If you only have three vowel sounds, chances are the language wants it to be maximally distinct from one another. If the system is /i/, /e/, and /æ/, then all of these are vowels that are pronounced with the tongue pushed forward, which makes them rather perceptually similar to one another. However, if the language has /i/, /u/, and /a/, then simply by articulating these sounds, one can feel the different tongue movements that are involved in these vowels, and then you can see that there is a huge difference between the three. Both /i/ and /u/ are vowels that have the tongue rather high, but /i/ has the tongue up front, while /u/ has the tongue in the back. And in contrast to those two, /a/ has the tongue rather flat at the bottom of the mouth.
Now, I suppose you guys now know why the dentist tells you to say "Ah..." whenever the dentist wants you to open your mouth. It is because this vowel forces your lips to be wide open, and the tongue is out of the way, not blocking your oral cavity.
So there. For the next factoid, I will talk about consonants. Ah, this will get very interesting.