Well, in general the languages which have cases are very strict about their usage in everyday life.
I cannot speak with 100% certainty for Finnish but I guess it would be the same as in Slavic languages (besides Bulgarian and Macedonian). If you use a wrong case, it sounds to a native speaker like if you said He am instead of He is.
I suspect that in Finnish it might be even more important, because while in Slavic languages we usually use preposition + case and the case is then often "grammatically redundant", in Finnish the same construct is often expressed just by the case without any preposition (or rather without any postposition :)).
So in Finnish using a wrong case not only sounds weird, it even significantly changes the meaning.
The whole meaning is defined by the cases. It's very different to say Syön autossa (I eat in the car) than Syön autoa (I eat the car).
It's just something that has to be learned, even though it can be very difficult at first if one has a native language without cases.
But how do you fathom exactly when the eating is taking place? It seems current to me.
For example, if David Attenborough was narrating a TV programme on mushroom-consuming animals (it could happen!) and he uttered the immortal words "The small animal eats three mushrooms" while we watched said animal chowing down ... wouldn't that be happening right now? It can't just be a 3-mushroom-eating creature?
Sorry - this is clearly turning my brain to mush XD ... I keep hoping that one day the partitive will somehow slot into place and it will all make perfect sense to me ... but this state of Finnish nirvana still proving to be elusive.
There is no 1:1 mapping between English present simple vs. continuous tense and the Finnish language constructs. The course would be MUCH MORE pleasant and motivating if you didn't bother us with your petty nuances, that you sometimes accept only continuous, sometimes only simple and sometimes both. Especially - I guess - that probably for most of us English is their second language and the small nuances in continuous/simple concept are something we are not familiar with either. Please let us focus on studying FINNISH. Now it is only very frustrating.
Surely it is possible for this sentence to have the meaning which is expressed in English by the use of the present continuous verb form - i.e "is eating". Does Finnish have anything which would allow a reader to know whether the present continuous or simple present tense is intended? If there is nothing in Finnish which enables a reader to make this distinction, the translation of "syö" in this sentence as meaning "is eating" should be no less acceptable than "eats".
I think I finally see the problem. "... eats" can both be equivalent to "... is eating" and to "...(habitually) eats". If we are lucky, the form meaning habitually is the one that is meant in the original sentence, and the "is eating" just goes with the partative. Anyone here who knows the answer?
I'm a native English speaker and "The small animal is eating three mushrooms," only really makes sense if it is eating all three simultaneously and hasn't yet finished any of them, which is possible, but definitely not what I'd assume.
In any case, as someone said above, in Finnish, that would be "Pieni eläin syö kolmea sientä," with a partitive object to indicate that we're not talking about the completion of the action.