Monster has an imaginary friend, which makes Robot question his sanity.
- Lucy (cameo)
- Master Grabmirist
- Perry (cameo)
- Crazy Cousin Gizmo
- Uncle Kuffley
- Gart (in picture as a kid)
- Fuzzy Slippers
- Robot's Crazy Cousin Gizmo makes his second and first official appearance. He was first seen in a portrait inside Gart's office in Blinking Light.
- The title may be a reference to the 1971 children's picture book Apt. 3.
- The mental asylum doctor shown for a brief second in this episode appears identical to the one featured in Doctor? No!, with the exception of sporting a more silver exterior.
- Kids are briefly featured in this episode.
- One of the baby pictures of Robot and Gart that Monster revealed from his wallet in Between Brothers is featured in this episode for a brief second.
- It is shown that the park can also be used as a golf course.
- Some of the objects displayed in Fuzzy Slippers' room were featured in precedent episodes:
- The stuffed toy Monster is seen playing with in one scene seems very similar to an Uglydoll.
- An exact duplicate of it can be seen in Fuzzy Slippers' room.
- One of the toys in Fuzzy Slippers' room appears similar to Lotso from Toy Story 3.
- The cursive 'R' that Robot temporarily wore in Spare Robot is briefly seen in the beginning of this episode during the scene when Robot and Monster are hanging their laundry.
- This scene shows that Robot doesn't necessarily have possession of clothing, as the only laundry they're hanging is mainly duplicates of Monster's pants and the cursive 'R' is the only article of 'clothing' belonging to Robot.
- This marks Uncle Kuffley's third appearance.
- Around the beginning, Robot quotes "Where's the box of Bacon-O's? It's part of my complete breakfast!" Bacon-O's is a parody of Cheerios, and he mimics the popular "part of a complete breakfast" speech required in all cereal commercials since the 1980s.
- While Monster was wearing the monocle to refer to his new maturity, he resembled the background Organic character who is often seen with a monocle as well.
- Robot's maturity machine is a reference to the Ludvico Technique from A Clockwork Orange.
Robot: (holding material) Wait, isn't this your security blanket? I thought you got rid of it.
Monster: There's a funny story there...(takes blanket and hugs it) I didn't.
Robot: Monster, you're too old to hold on to your blankie.
Monster: Reminds me of my childhood. You won't understand because you hate being remind of your childhood.
Robot: (slightly fuming)
Monster: I say children, it's a sidewalk, not a side-run. (chuckles)
(after Monster tosses his blanket into into the trash chute)
Robot: You did it, Monster. I'm so proud of you.
(gasps in shock when Fuzzy Slippers passes by the kitchen)
Robot: Monster, did you see that?
Monster: I assuredly not. I'm far too mature and sane to see imaginary people. (Worriedly) Why, do you?
Robot: (nervously) Yes, I do...