^But that doesn't make much sense for some cats. Some always make a short chirpy noise instead of normal meowing - I have such a cat. He's not making the chattering noise over birds, it's just a high pitch...well chirp. It sounds something between a bird chirp and him saying "oh oh oh".
This is his general use meow for everything, it makes him look cute and he knows it.
And in the case of that book, they're calling the brrr noise a trill. If you want to further complicate this I have one that doesn't brrr, he makes low barely audible hrrrm noise.
These noises are not just used in greeting, though. Many house cats will use this noise when excited, happy, or just as general use.
Since everyone calls the same noises different things, I prefer to use a more onomatopoeia method of describing them.
Of course with your own cats, your best factor for actually figuring out what vocalizations mean in each cat (each cat has it's own habits) is to watch your cat's body language and use it's current activity to help figure it out.
