Simon J. Gerard of "Starburst" magazine regards the secondary title sequence – in which the Mysterons, represented only by their "strange green light beams", announce their latest threat to Spectrum – as the "defining moment" of the original "Captain Scarlet". The authors of "The Rough Guide to Cult TV" argue that for younger children, the aliens' slow, deep voice "seemed to embody evil." Several commentators argue that the fact that the Mysterons remain unseen, preferring instead to operate through their replicated intermediaries, makes them all the more frightening. Digital Spy's Morgan Jeffery calls the Mysterons' invisibility "a masterstroke, and another reason why "Captain Scarlet" holds up well to the scrutiny of an adult eye. The Hood from "Thunderbirds", "Stingray"s Aquaphibians - these are characters unlikely to disturb the dreams of any but the very young. The Mysterons, though? The images conjured up in the minds of older children with over-active imaginations would have been far more terrifying than anything Anderson and his team could have hoped to construct."