Why not zwierzęta? Is it not Accusative after 'She sees' or does tamto affect it?
It is Accusative, but it's one animal (that old animal), and not many. "zwierzęta" is plural, "zwierzę" is singular.
I think i was overdoing it and got confused. I realised my mistake after. Read up on Accusative case and only just realised neuter accusatives are identical to nominatives. That's useful to know!
When we learn orthography, we rather talk about "rz wymienne na r" (so situations when rz turns into r in another form), to distinguish the words written with rz from those written with ż.
I'd say that what you're asking about happens in the 'masculine personal' forms. Those forms are always kinda different, softened. So for example 'wysoki' turns into 'wysocy', 'młody' into 'młodzi', and 'stary' into 'starzy'.