- Author's Saving Throw: In the afterward for Zoe's Tale, Scalzi admits that a major motivation to telling a parallel story was to make Zoe returning with exactly what the Roanokers needed feel like less of a Deus ex Machina. It also let him give some closure to the werewolves.
- Old Man's War, as an homage to Starship Troopers, was naturally committed to a Crapsack World view of the universe in which humanity's only options were extinction or perpetual warfare against any race capable of occupying Earth-like worlds. (Though even in that book, the Straw Character 'has a point' and the Consu clearly aren't following the CDF's script.) The Ghost Brigades and The Last Colony invert this bleak worldview entirely, suggesting that many alien races can come to long-term peaceable agreements about territory - which leaves the CDF an example of Humans Are the Real Monsters.
- Many aspects of Old Man's War can lead to some rather nasty Fridge Horror regarding just how certain aspects of the Colonial Defense Forces work, in particular the use of Brain Uploading to extend life by transferring a human's mind into a Blank Slate clone, or the use of enhanced Blank Slate clones sans personality to create what are essentially Child Soldiers. The sequel, Ghost Brigades is largely an exploration of much of this Fridge Horror to show that many characters In-Universe have similar concerns both about the Super Soldier program and the state of humanity's foreign policy.
- Fridge Brilliance: When Perry's squad is sent to run a seemingly outrageous distance in an hour, it is mentioned that the slowest runner (who still met the deadline) was one of the handful of the recruits who had previously served in the military on Earth. Why would he have the most trouble despite having a new superhuman body? Because he probably has the most experience running, and thus has ingrained habits regarding how he runs, to include pacing himself on long runs. Either he doubted he had the actual strength and endurance to perform at that level, or he figured out how fast he needed to run and saw no particular reason to run faster. The latter explanation makes even more sense if he figured Ruiz was going to find some reason to lean on them harder anyways.
- When John sees a boy he doesn't know put an arm around his adopted daughter Zoe, he gets ready to intervene. Jane stops him by wrapping her own arms around him and teasing him. The difference in responses might be chalked up to the very libertine attitude that Special Forces soldiers have about sex, given their being born as adults with no childhood integration into society. It's just as likely that Jane enjoys taking the piss out of him from time to time.
- Nightmare Fuel: The Salong, an intelligent species with similar appearance to the deer:
Now this little fucker is a Salong. Our first official encounter with the Salong happened after we tracked down a rogue colony of humans. People aren't supposed to freelance colonize, and the reason why becomes pretty obvious here. The colonists landed on a planet that was also a colonization target for the Salong; somewhere along the way the Salong decided that humans were good eatin', so they attacked the humans and set up a human meat farm. All the adult human males but a handful were killed, and those that were kept were 'milked' for their sperm. The women were artificially inseminated and their newborns taken, penned and fattened like veal. It was years before we found the place. When we did so, the CDF troops razed the Salong colony to the ground and barbecued the Salong colony leader in the cookout. Needless to say we've been fighting the baby-eating sons of bitches ever since.