I'd have to say it's the connection, the feeling of uniqueness to it, the instincts, the rawness, feeling of doing something considered taboo and unconditional love behind it all as well. More often than not, your fluffy friend is going to be a much better partner than a human, even without taking the sexual aspect into it. Adding the sexual aspect into it just elevates how much better they are. Not that I'm solely into animals mind you, people can bring things that animals cannot and the same applies to animals when compared to other people. It's just way easier to love your furry friend