@Blue_Skyesr_here
I believe it was "The Enemy Within", and the #CinemaDogs pup was (unfortunately) an experimental animal sent through a malfunctioning transporter to fuse two otherwise identical animals with distinct personalities back together into a single animal. The restored single animal died, but they thought that the two Kirks could process the situation and survive as a single Kirk. #StarTrek folks help me out here. 🖖