In this episode, Andy tells Dr. Thomas Petersen his address is 14 Maple. In season 2 episode 18 "Jailbreak" Barney tells Mr. Horton that Andy's address is 24 Elm Street. In season 3 episode 24 "Aunt Bee's Medicine Man" Aunt Bee tells Colonel Harvey their address is 332 Maple Road. In season 4 episode 16 Opie starts to burn their address on the house starting with "3."
Andy invites the Doctor to dinner and tells him the address to his house, "Just off Main Street, 14 Maple."
When Andy looks at Dr. Petersen's (we see on his sign he hangs outside his office that his name is spelled with an "e" and not an "o") diploma, it's from John Hopkins University.
William Christopher appears in this episode as 'Dr. Thomas Petersen.' He also appears in "Aunt Bee on TV" as 'Mr. Heathcote,' from the Internal Revenue Service.
William Christopher later appeared with Ronnie Howard in the M*A*S*H episode Sometimes You Hear the Bullet.