His body changes

Before he can respond, Isaac felt his new body changing. Everything about it, pretty much, reverting to how it had been before he had swapped. He ran to the bathroom and looked into the mirror. He didn't see his old self there. Rather, it was a version of Zach that matched his former body type. Even his dick was now shrunk to his old proportions.

He left the bathroom to see Mia on the phone. Her head turned to look at him and she glared. She whispered something, and the tingling returned.