I think one of the few things that still bothers Juuzou is animal cruelty.
We know because of his Birthday Poem he was given a pet to care for, allowed to form a bond with it. (Likely the only thing aside from Mama he was allowed any sort of bond with. And definitely the only thing that loved him without sinking its teeth in) Then he's forced to kill it in a very hands on and personal way- strangulation. I think it's safe to assume this was the first life he was made to take.
- Cause once you kill something you deeply love and connect with, repeating the act on a nameless victim is far easier, even if that victim is anther human. (I doubt he felt humam by this point anyway)
Outside of this occurrence I doubt he was made to do it again, theres no real point to it. Once you amp it up to homicide why go back to just animals? Plus, he's not going to allow himself to form any more bonds now Mama's cemented that anything he loves - aside from her, can and will be taken from him, and he will likely be made to participate in its destruction. (Also helps keep him in line. He is her pet afterall. He could easily find himself on the receiving end)
So, hes doesn't become numb to it like he is with people. Human suffering is a daily occurance, it's completely normalized to him. This isn't.
By the time he's "saved" (repurposed) by the CCG and sent to the academy he doesn't seem capable of expressing many emotions beyond the occasional spike of, at times, homicidal rage. But of course, that doesn't mean he doesn't feel anything.
- I think he was clearly unsettled discovering Tokage mulitating cats. Infact I think the man downright terrorfies him. Because he spent his childhood in the hands of people (well... ghouls) like Tokage. He knows he'll make good on the promise "If you tell anyone I'll kill you." Plus he knows nobody would believe him anyway. So whats the point? He'll take on the label of cat killer just as he has taken on whatever labels and rolls where forced onto him before. (I don't think Juuzou is allowed to truely feel his fear. Or much else for that matter)
And lastly. He likes animals, we know this, we are shown very clearly that Juuzou loves animals. The one time were shown what he does in his spare time he's at the zoo drawing animals.
Abused people often gravitate towards animals. (Neurodivergent people do as well- personally I think he's both Autistic and ADHD but thats besides the point) Animals do not hurt you the way people do. If one hurts you it's ether being forced too by a human, or defending itself.
I think he sees himself closer to animals then he does humans or even ghouls. (I think he views himself as a fight dog but thats for anther time.)
