I have had similar. Most of mine however are me being passive, like i'm just watching a film - not me but other people commiting violent things. Rarely I see myself doing anything. It is frightening and horrible and hard to switch off. My dad said he has sometimes had horrible bad words in his mind that do not come from him - my dad never ever swears, so for him this is so against his character.
The only way I can explain these thoughts is a loss of control or a fear of loss of control - of yourself or other people losing it. Its part of anxiety I think, it affects your thoughts and images in your mind you don't choose or want.
The point is - it concenrs you, you love animals and you are in control of your actions. The thoughts you are getting is an extension or exaggeration of your fears - losing control, especially the things you hate the most. For my dad and myself - it is things we hate the most that goes through our minds. It gets you off-guard though doesnt it, like when you're not even thinking about anything, do you find this too?
What I try to do is rationalise it, say "this isnt me, it is my anxiety" and I try to think of something positive and nice. I try to not worry about it and it soon passes. You're not going mad because you are aware of these thoughts, and you are aware it is not who you really are. Hold onto that.