Re: Cases

"I understand that masculine animate nouns don't change."

Actually, you've got this backwards. Masculine animate nouns do change; inanimate ones don't. Happily, there's a logic behind it, so this isn't just something to memorize.

Remember that Russian word order is very fluid because of its highly inflected case endings. There's a subtle difference in emphasis in sentences like "The flowers are on the table" and "On the table are the flowers," but both are equally grammatical. This flexibility extends to sentences like "человек укусил кролика" ("The man bit the bunny rabbit"), which can also be written "укусил кролика человек" or "кролика укусил человек" without a fundamental change in meaning. In situations like this, where you have two animate nouns, it's pretty important to know who is biting whom, since the nouns could come in either order. If it was a pairing of animate and inanimate: "человек укусил бутерброд" ("The man bit the sandwich"), the object is inanimate, so its ending doesn't change, but the man is the only one in the sentence who could be doing the action, so the meaning is still clear.

Does that make sense? (More to follow . . .)