I think a subtle misunderstanding underlies this question. Accusative case forms for masculine animate nouns may share genitive case forms, but they are not in genitive case. Of course, this distinction doesn't have much practical significance, except when people (and, frankly, this is one of the mistakes I make most often) extend this to tying to use genitive forms for the accusative case of singular feminine nouns, of which мышь is one. Obviously, this issue is further complicated by the gender of words ending in -ь not being immediately obvious. If the cat were nibbling on a deer, it would be оленя, for instance.
Yes piguy, I worded the question poorly, but you captured what I had been going for perfectly - if I had worded my question better, it would've been "Can't the accusative form that looks like genitive be used here since 'mouse' is animate?" Later I looked up мышь at wiktionary and learned that it's feminine, so it retains its form in the accusative - again, exactly what you've observed above. Have an upvote!
Good thing piguy was here to help out :-) By the way, note that the accusative = genitive rule still applies in plural, even for feminine nouns - accusative plural is мышей, not мыши.
I put "The cat near the bed is eating a mouse" and was marked wrong.
I take it this is simply because there is a different way to express relative clauses that we haven't learned yet?
I don't think "the cat near the bed" actually contains a relative clause (an adjectival phrase I think), but I do believe you are correct that that would likely be translated using a relative clause in Russian.
Why do you use passive tense so much when translating into English?
Passive tense reads best in Academic Papers.
No, I don't. "A cat is eating a mouse" - that's active voice. Passive voice would be "A mouse is being eaten by a cat".
How would you propose to translate this sentence differently, anyway?
There is emotional content involved - a previous poster said, "Gross".
Why should a mouse get special treatment in grammar?
Experiment with other types of foods. (For example)
The cat eats kibbles. Where does the cat do it? Near the bed, the cat eats kibbles.
Near the bed, the cat is eating kibbles.
Yes, OK, but why the hushed voice?
If you don't believe me, you could read the link I provided about passive voice.
I read it. And I repeat, this isn't passive voice. The difference between "a cat eats a mouse" and "a cat is eating a mouse" is present simple as opposed to present continuous, nothing to do with active vs. passive. In both cases, you have the actor as the subject (cat), the action (eats/is eating), and the thing being acted upon as the object (mouse). Passive voice is when the thing being acted upon becomes the subject - as in "the mouse is being eaten by the cat". Honestly - if I say "I am eating breakfast right now" are you going to tell me that I should have said "I eat breakfast right now"?
Russian does not distinguish between present simple and present continuous, so either is a legitimate translation here, though present continuous is a more probable sentence. For the difference between present simple and present continuous, you could look at, for example, these two pages: http://www.perfect-english-grammar.com/present-simple-use.html
I read your link.
From it (emphasis mine):
The passive forms of a verb are created by combining a form of the "to be verb" with the past participle of the main verb.
"Eating" is not the past participle of "to eat", it is the present participle. "Eaten" is the past participle and I don't see it in the English here at all. I do see "eating" (again, present participle).
You seem to be focusing solely on the "to be verb" aspect of the formation and not on what actually informs the construction of the passive (the past participle - which is displayed pretty clearly in the chart below the line I quoted from, again, your own link trying to prove your point).
Why are you so belligerent (I don't just mean here, I mean all over the boards recently)?
There's no need for it.
You're seriously unpleasant.
You are using Russian grammar to define English grammar.
I thought we were learning (passive tense in English) Russian into English?
AND I have NEVER been a grammar nazi.
I do not want to learn English grammar in Russian, nor do I want to learn Russian grammar in English. They are two different grammars.