Most of my creatures start with some basis in the real world, usually obvious in their construction. However, I don’t really set out on these sketches thinking “I’mma draw a rat crossed with a Christmas tree.” I just start with one part of the animal, usually the head, and see what happens. Some days, I might actually feel like drawing just a rat and leave it at that. Other days I find that rat ears are an interesting place to start, and what else is interesting today that I could throw in there?
I think most of my art is really an attempt to combat the boredom of everyday human survival, and even combining rats with Christmas trees scratches that itch.