Charles Aidman is also in "And When the Sky Was Opened." He later was the narrator for the 1985 version of the Twilight Zone.

Tracy Stratford was also in "Living Doll."

Composer and musician Bernard Herrmann is credited for his musical score in the opening credits, above the writer and director credits.

Writer Richard Matheson named the characters Ruth and Tina after his real-life wife and daughter.

Matheson based his teleplay on his own short story "Little Girl Lost," first published in Amazing Stories (November 1953).

Opening Narration
Narrator: Missing: one frightened little girl. Name: Bettina Miller. Description: six years of age, average height and build, light brown hair, quite pretty. Last seen being tucked into bed by her mother a few hours ago. Last heard - aye, there's the rub, as Hamlet put it. For Bettina Miller can be heard quite clearly, despite the curious fact that she can't be seen at all. Present location? Let's say for the moment, the Twilight Zone.

Bill: Another few seconds and half of you would have been here, and the other half...

Closing Narration
Narrator: The other half where? The fourth dimension? The fifth? Perhaps. They never found the answer. Despite a battery of physicists equipped with every device known to man, electronic and otherwise, no result was ever achieved, except perhaps a little more respect for and uncertainty about the mechanisms of the Twilight Zone.

When Bill throws a coin at the wall it freezes before disappearing through the wall.

When Rod Serling does the opening narration, the boundary marks that Bill will draw later in the episode are visible just over the bed to the viewer's left although in black rather than white.