"Ah, yes, a promise is a promise. Now... how much do you want to be a bird? Do you just want the body of a bird? Or do you want bird thoughts as well? What about bird memories? Would you like to be a bird in every way for a little while, and hunt and think like a bird does? Or does Yufei simply want to wear a different skin for a while?" He seems to be fine with offering all of these equally.