A joke in the traditional manner

I was told yesterday by an eight-year-old informant that this joke’s premise is already on the wane: “The brainrots wanted to make a fresh start.” So before the sell-by date recedes further into the past:

What number went to see the doctor?

No spoilers; the punchline is in the comments.

Related reading
All OCA jokes in the traditional or neo-traditional or non-traditional manner

[“In the traditional manner”: à la my dad, who was making dad jokes long before they were called dad jokes.]