But the food doesn't have to be of the animal... Imagine a group of zoologists in a rainforest. A gorilla starts to eat one of the female scientist's meal. And somebody says: "The animal is eating her food."
I'm just trying to understand the reason why it isn't correct. Because I can't see any reason right now.
Sometimes when you get new words you really do need to read the "explain this" that pops up when your hover over it. When using a possessive in Italian, the gender and plurality of the possessive should be in line with the object being "owned", not the person doing the "owning" So "his monkey" is "la sua scimmia" because the Italian word for the monkey "la scimmia" is feminine. It does not matter if we are talking about a male who owns a monkey, because "la sua" can mean his, her, hers, or its. As well, "il suo" can mean his, her, hers, or its, but it should only be used when the thing (noun) being owned is plural and masculine. Ex: her dog- "il suo cane"
If the gender of the animal is unknown, in English we would use "its food". How do you know the gender of this animal, when we do not even know what kind of animal it is? If the animal is eating the little girl's food, then it is said the same way, but shouldn't there be more information then. Normally, we work with the information we have. So far, just an animal...
The object of this sentence seems really unclear to me. Is "suo" referring to the animal eating its own food, or to the animal eating someone else's food? Is there any way to tell from just that one sentence? And if the gender is ambiguous, why isn't "their" an acceptable possessive pronoun? Are you only allowed to use that in the plural sense?
"Suo" is referring to the animal because that is the subject of the sentence. For this sentence, the gender of the animal is ambiguous so we would use "it" to signify that ambiguity. Once we are given the gender of the animal then we can start using his/her. If the animal was eating someone else's food it would be something like this "l'animale mangia il cibo di lei (the animal eats the food of hers; direct translation)". If the animal is eating it's own food it would be "l'animale mangia il proprio cibo (the animal eats its own food; remember we don't know the gender of the animal yet).
The reason why "their" is not accepted is because "their" refers to a group of of things and it would be expressed like this "gli animali mangiano il loro cibo (the animals eat their food).
Hope this is helpful