Amazing job ! I love your design and the shape you gave to the rat is very interesting. The animation is clean and smooth, it's very hard to find something to say to be honest

To be very picky I would say maybe your animation could use a frame like this where the legs are crossing :

Then it comes probably to personal taste but maybe you could have a smoother movement for the legs ? For instance I find it a little bit choppy when the back leg goes fully extended. You could try also give more impact by squeezing the body of the rat a bit more when it reaches the ground.
I did a quick redraw over your animation to show you better what I mean here. I hope it helps !

Looking over internet to find reference of rat running I found this video which can probably be useful to you if you didn't watch it yet.
https://www.youtube.com/watch?v=MEQYjEWBfWgAnyway as I said, I am being very picky here. Your animation is already working pretty well. I hope you share with us the final version once it's done. Keep up the good work !