This episode marks the second of two UFO appearances by Anglo-Australian actor Tom Oliver, who plays the SHADO technician who drills into the alien transport capsule. It is also one of the four appearances by Italian actor Gito Santana, who plays the alien. Although only credited by name in two of his appearances, in one sense Santana became the "face" of the series, thanks to the fact that he played an alien in the pilot episode. His face is seen in closeup in the opening shot of the title sequence, showing the alien's contact lens being removed.
The red mini dress worn by Susan Jameson (Anne Stone) in one scene, would later appear worn by Deborah Grant in The Psychobombs (1970) and again in Timelash (1971) worn by Kirsten Lindholm.
First appearance in broadcast order of Andrea Allan as Moonbase operative Carol Miller, possibly to replace Gabrielle Drake as Lt. Ellis.
In the exterior scenes involving the tramp Ben Culley (Nigel Gregory) and his dog, all the audio was evidently added in post-production, and the sound of Culley's dog's barking was evidently impersonated by a human voice artist.
Deleted scene: Another hippy (Joe) from the group Culley's a member of informs Culley that he's been ousted from the group for being a "bad scene".