The cat that keeps appearing at the window of the hideout is the same cat Audrey Hepburn looks after in the movie Vittorio Barino.
Robert Hogan and Diana Hyland worked together less than a year earlier in Spur of the Moment (1964).
The title is a line from the lullaby "Rock A Bye Baby."
Born within just a few months of one another, Diana Hyland and Sue Randall both appear in multiple episodes of this series, this being the only time they appear together. Tragically, they also both died in their 40s from cancer.
This is the second of three appearances Sue Randall makes in the series, the other two appearances occurring in Nightmare at Northoak (1963) and Wings of an Angel (1965).