sounds like you might have extra faces or vertices around that area... You can also delete one small row of faces around the area where the tail meets the body and then double check the faces edges and vert's to make sure you dont have extras. Then exturde over again and re merge.
I am enough of an artist to draw freely upon my imagination, knowledge is limited, imagination encircles the world. (Albert Einstein)
https://www.artstation.com/kurtb