cat's meows

My cat has a few type of meows.

• the regular meow
• the purr meow combination (sounds like a pigeon cooing)
• and a low sad sounding meow when he thinks I'm not there.

These are the only ones that I've heard from him so far. Does anyone know what these sounds actually mean?
It seems that the regular meow is to signal for someone's attention.
The sad sounding one seems like he is unhappy.
What are some other ones that people have heard? What do they mean?

My parents have a Siamese cat -- we'll call him "Bob", to protect the innocent -- who is now twenty years old, but in his younger days he was a hell raiser. We are told that Siamese cats are "very vocal". That's objectively accurate, but it fails to convey the experience of having a damned soul singing an aria of despair in your stairwell at 3:00 AM.

My parents' stairs have great acoustics. "Bob" must understand this, because he used to go there and hold forth for half an hour at a time. The only word I can think of is "woodshedding", and this is where I begin to anthropomorphize. It would take much longer to explain this if I just described the phenomenon in neutral terms.

He would emit a drawn-out agonizing howl of despair, several notes long, and then repeat it. With minor variations. Then he'd try the first one again, and go back to the second. He'd take that one, and cultivate it further. Or maybe he'd abandon the second, and start modifying the first in a different direction. When he got something perfected, to a point where he really liked it, something really blood-curdling and spine-chilling, he'd repeat it several times. And then he'd start all over again. This would go on for half an hour or so. If he repeated himself, I never noticed it. That cat didn't do this "meow meow" shit. He was an artist.

I make no claims about the cat's "motives", nor do I claim that a cat can even have anything like what we understand as a "motive". It's unknowable. Cats can't talk. We can't get inside their heads. So I really have no idea what was going on in that little pea-brain of his, but I can say with certainty that he was, and remains, a damned peculiar animal.

First, my parents' cats..

Spike - The cat that thinks he's a dog. That's right. He sleeps like a dog. You can carry him around like a puppy. His only meow is a questioning, short mew.

Charlie - The female cow cat with a gender crisis. She's a bitch. No, really, she's all friendly and "love me, love me" one moment, and then all claws and hissing the next. She only howls meanly.

Max - the black kitten. I think his full name should be Max Power. He comes when you call "little buddy", and only makes little kitten mews.

Ivan256 and I only have one cat. Her name is Samantha, she is about 2 years old. She was the runt of the litter though, so she's only about half the size of a normal cat. She is also as DUMB as a kitten, she STILL eats ANYTHING, and she is only capable of the small, cute, adorable kitten-sized "mew".

Oh the excitement...