I read this again because volume 1 is coming out in my country but I can't buy it since it's only paperback. I really hope that they release it in ebook form.
Geuroo wants to say 변신 = transformation but ends up saying 병신, 병신 is similar to r-word but it can be used to call someone a fool. 병 means bottle so that's why it's censored like this.
porn logic: you have a muscular body but don't have enough strength to climb the stairs but you have enough strength to fuck in the staircase