Lieutenant Green's reaction to Rhapsody's death is especially heartbreaking. Trying to contact Rhapsody, sounding like he's about to cry.
Uncanny Valley: The puppets falls into this now and again. Gerry Anderson himself noted this, and found it to be something of an uncomfortable point between realistic enough, and seemingly trying too hard to imitate human movements.
What Do You Mean, It's for Kids?: The series is perhaps the darkest of Gerry Anderson's series, with a large bodycount (for a series of its kind) in each episode, occasionally reaching double-digits. Many of these deaths tend to be rather gruesome, too, and oftentimes show deaths in full gruesome detail. Hell, the first episode alone featured Captain Brown being used by the Mysterons as a suicide bomber.