a. There is no seam. We've finessed the seam so thoroughly, you can't even tell. This doctor knows everything about the situation as seen by the last doctor, no need to worry about the handoff. You can't tell where one part of the railing ends and the other begins. Your place in the queue and your records and your status are so clear to the next agent that it won't matter a bit to you that there was a switch.
b. There is a seam. That was one color, this is a different one. That was yesterday, this is today. She was your last teacher, I'm your new teacher.
As you might have guessed, the problematic area is where you try to hide a seam, and you fail.