I Just Shot Marvin in the Face: Deserves a special mention, as he uses his guns for everything from pushing open doors to scratching his nose. At least he's smart enough not to use the barrel for the latter.
Not with the Safety on, You Won't: An interesting variation, where an enemy mook gets a hit in on him and uses the opening to pull a gun. The gun fails to fire. A now-recovered Oktavian explains "Machine empathy..." and whacks the mook with his power axe.
Body Horror: After being Mind Raped by a daemon. The fact that his stammered prayers start manifesting Voice of the Legion is the first bad sign. He primes a grenade to commit suicide, but before it goes off there is a brief shot of him collapsing and starting to grow tentacles.
Accent Adaptation: A reverse example. Makkabeus speaks very formally (addressing Lechias with the polite pronoun "Sie" even though they are already well aquainted). The English subtitles rather amusingly translate this as Ye Olde Butcherede Englishe
Alternative Character Interpretation: Is he misguided in trying to capture G'gour to use against Chaos, or was the daemon's return inevitable and capturing him the only way to save the planet? This nicely mirrors the Puritan/Radical divide present across 40K.