Why do cat's hiss?
I have read that when cat's hiss they are mimicking snakes. Cat's imitate snakes because most other animals including dogs are afraid of snakes. So, when cats hiss they are attempting to scare away another cat, dog, or other enemy. A cat will actually attempt to take on a snake like appearance. The cat will flatten out his ears, widen his jaw, and wave his tail back and fourth before he hisses to scare away the enemy. Sometimes the cat will spit when they hiss, which is similar to that of a snake when they are excreting their venom to paralyze their victim. This is a cats way to communicate... What ever you do, do not mimic the cat and hiss back. Hissing at your cat might scare him (remember he uses this to scare others) and if you scare him, he might become afraid of you and you will not have a good relationship or the relationship you would want with your cat. So, take the warning and give him space, if he hisses at you.
Just a little fun bit of trivia...