I am confused. Isn't "pies" masculine personal? So shouldn't it take Genitive when plural accusative.
I don't know if you confuse stuff or if you just phrased it in a strange way. Accusative can 'look like' Genitive, 'be identical to' Genitive, but it will still be Accusative. And that's how one has to look at it. Anyway:
"widzieć" takes Accusative
"pies" is simply masculine (we only care about the notion of 'personal' in plural. In singular, the notion of 'animate' is important in masculine Accusative)
and in plural, as dogs are not persons, it's 'not masculine-personal'
And the 'not masculine-personal' plural looks has its Nominative and Accusative form identical.
If it was something 'masculine personal', like boys or people, then indeed Accusative would look the same as Genitive.
Pies is a very odd word in PL. Pies, psy, psów, psa... - the endings change so much that it looks nothing like the original word
Actually, it's not odd at all, and these changes are completely regular… It's just that it is way simpler to pretend that they are not(ie. treat them as exceptions), than explain the yer reflexes, which might require couple of years studying Linguistics/Phonology/Phonotactics and then a few months of crash course of Slavic development since Proto-Slavic to understand. ;P
It's the same in Russian--pios, psy, psa, psow, psam, psom, psami, psje, psach, nothing odd or unusual about it. Just Slavic declensions, except pios is an old-fashioned, literary term in Russian. Sobaka is the common word--sobaka, sobaki, sobak, sobakam, sobakoj, sobakami, sobakie, sobakach