The sea-diving ghost's roar came from the "Abominable Snowman" sketch of the second episode of Stan Freberg's 1957 CBS radio show.
The only episode in the series to not have a laugh track.
Last episode to feature the short-lived static title cards that were customized to the story. Subsequent episodes would have the more familiar animated standard title card.
It is not until late in this second episode of the series that Fred's name is mentioned for the first time.
When Velma is reading a spell book in Widow Cutler's house, she makes the remark, "Veeery Interesting". She's doing an impression of the popular catchphrase used by Arte Johnson on Rowan & Martin's Laugh-In (1967).