When James Caan walks by a paperback spinner rack, a paperback title "Ruined Virgin" can be seen. It appears that this is not a real book. This book has only been seen in the movie The Swinger (1966) with Ann Margaret. There is a scene where Ann Margaret dances with the book in hand and you can see the cover. Margaret also reads the cover aloud. It appears that the book was a prop in the movie from 1966 and later reused for Slither in 1973.
The van is a 1973 Rec Trans Discover 25 R. It was based on a Dodge platform. The body was all fiberglass and the vehicle weighed five tons and got 10 miles per gallon.
Peter Boyle does an imitation, singing, and James Caan gets it quickly, saying "Mr B." which referred to Billy Eckstine, the song "Everything I Have Is Yours".
This film opened in Great Britain at the same time as another Sally Kellerman film, the musical remake, Lost Horizon (1973), of Lost Horizon (1937), which was that year's Royal Command Film Performance, attended by Queen Elizabeth II. Sally Kellerman told several interviewers that she thought the Queen would have a far better time at this movie, although whether, as legend suggests, she said the same thing to the monarch herself, is not certain.
The huge cab in the beginning of the film is a 1946 DeSoto Taxicab, model S-11. It could carry six passengers in the back with jump seats. It was the second most popular cab in the country, behind only Checker.