The Manhattan Project/Trivia

Hey, It's That Guy!: quite a few, actually.
- Dr. Mathewson gets around in the scientific community. You'll recognize him as:
  - Joe Huxley, the University of Kansas science professor from The Day After.
  - Dr. Walter Curnow, who built the ill-fated Discovery spacecraft
  - Dr. Emilio Lizardo / Lord John Whorfin
  - John Valentine, a computer scientist who has Trouble at 35,000 Feet in Twilight Zone the Movie.
  - Dr. Dick Solomon from 3rd Rock from the Sun.
- Paul's girlfriend is a teenage blond Miranda.
- Paul's mom spent the next eight years as lawyer Ann Kelsey of McKensie, Brackman, Chaney and Kuzak.
- Paul's physics classmate Max is an almost unrecognizably young Dr. James Wilson.
- Frasier's dad is an Army colonel!
- The kid at the science fair who invented a way for humans to use insects as dietary supplements has had one-off roles on a number of TV shows ever since, including Mad Men, The Closer, Wizards of Waverly Place, Lie to Me, Law and Order, Weeds, Medium, ER, and Charmed.
- Nathaniel Fisher is Miles, the Radiation Controls Officer. He's a little hard to recognize because here he actually has hair, and it's brown, albeit noticeably thinning on top. He also has a mustache. If you are still asking Who Is This Guy Again?, he's the one who tells Lithgow that he has to report the missing plutonium. When they work to disarm the bomb, he's usually in the vicinity of John Mahoney (Frasier's dad).
- According to IMDB, '80s teen pop star Debbie Gibson appears as an uncredited extra in this movie, about a year before she made it big in 1987.