This is the 5479th most frequent Japanese word.
うしろ足
"うしろ足" means "hind legs."
The word 'うしろ足' refers to the hind legs of the cat in this context, used to indicate the rear legs as compared to the frontal ones.
うしろ足で立つ猫は芸術的ですね。
A cat standing on its hind legs is artistic.
Here, 'うしろ足' specifies the part of the dog that is injured, identifying it as the hind legs.
怪我をしたうしろ足を庇っている犬を見た。
I saw a dog favoring its injured hind leg.
In this sentence, 'うしろ足' highlights the strength found in the hind legs of the rabbit, focusing on their physical characteristic.