Medical school entrance exam

[LONDONER]

I found this on the web so it does not refer to me:

When I was younger gave some thought to attending medical school, but I was confused and confounded by the entrance exam.

The deciding question was, "Re-arrange the letters P N E S I to spell out an important part of the human body that is more useful when erect."

Those who spelled SPINE became doctors.

The rest became attorneys, and are now in Congress