I wondered why my cats have different tone purrs (2 of them purr at 2 different levels), why they sometimes "knead" on me (like they are kneading dough ) and why the male suckles my neck

To answer your first question, I found out that cats will meow in different tones to speak with other cats to tell them different things.That even includes you sometimes. I haven't found anything on the purring yet, but I try to find out. I will try to find type answers to the others too.
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Now heres a question I need help on. Usually when cat is happy, they will purr. Well my cat does too, but sometimes even when she is in a bad mood she will purr. I don't get it. Why would she do that?

Another question: My cat always seems to flip her tail up and down when she is angry, is she telling me that she is angry?