The film was released in the USA as "Beyond the Door II", although it has no connection with "Beyond the Door" (1974).
The popular blue poster for "Shock" (1977) with the long-haired woman holding a bloody box cutter peering from behind pieces of wood, appears to have been appropriated (with a few modifications) from the 1963 paperback cover art by William Teason for Shirley Jackson's novel "We Have Always Lived In The Castle".
Though this was the last film Mario Bava made, it was not the last film of his that was released. That honor lies with Rabid Dogs which was released in 1998.
Filmed mostly in June 1977, the film was hurried and already released in Italy in August 1977.