I think it depends on the slave/pet. How do you feel inside? What energizes you? How do you respond emotionally? How do you feel at your most raw state? I had the same challenge myself. The first real role play I did was as a dog and I had slave sisters in the same "litter". They made me feel so comfortable in my own skin, even though this was all online. Those moments always stuck with me and that was years ago. Since then, I've been broadening my experiences past just being a pet --- BUT I ALWAYS GO BACK TO IT!! I love being my Mistress' pet and i do see myself and express myself as a pet. It's just something I deeply connect to. I wear a tail every day, practice dog tricks, and eat dog food periodically, among other things to harvest that pet mindset and give my Mistress what pleases her.

Whatever works for you and you identify with, don't be ashamed or concerned about technicalities. Just explore Hopefully that helps!