If you don't get the joke, I don't blame you. It does require some context. Sandra (middle) is ordinarily a human, and Woo (left) a raccoon. Lilith (right) is a prodigy magician from Gaia, Sandra and Woo's sister webcomic. Although she doesn't often make this kind of error, it seems she's unintentionally switched these two friends' species.
Sandra and Woo is a wonderful webcomic (you can see it in the list on the right). Like xClassicalCatx, they are having a fanart contest, into the which I will be entering this. I plan on making more entries, but this was the first idea I had.