I've heard as well that some animals, like Gorillas, have a hard time understanding human speech. However, they can communicate in other ways (using simple sign

I've heard as well that some animals, like Gorillas, have a hard time understanding human speech. However, they can communicate in other ways (using simple signs) that make it clear they have some understanding of language (in the sense of concepts like position, individuals, etc.) and context. To me this suggests either their sound processing is also insufficient to understand human speech, or not their vocal anatomy, I wonder, but their auditory anatomy could be not ideal for understanding human speech.