The detective inspector of the novel becomes an undercover green grocer, the sleazy tobacconist/magazine shop becomes a neighborhood cinema in the film, and the mystical younger brother emerges as a somewhat mentally challenged young man.
Some erroneous modern sources identify Sara Allgood as the uncredited actress playing the bird shop customer, but she does not appear in this film. The identity of the actress in question is presently unknown.
The failure of the original copyright holder to renew the film's copyright resulted in it falling into public domain, meaning that virtually anyone could duplicate and sell a VHS/DVD copy of the film. Therefore, many of the versions of this film available on the market are either severely (and usually badly) edited and/or of extremely poor quality, having been duped from second- or third-generation (or more) copies of the film.
In "Inglourious Basterds" they say that film is three times more flamable than paper. They show a boy asking if he can bring film onto a bus and the bus driver says "You can't bring that on here it's flamable." That seen is from this movie.
The trivia items below may give away important plot points.
In The Dick Cavett Show: Alfred Hitchcock (1972), Alfred Hitchcock revealed that he made a terrible mistake with "Boy with the Bomb" Suspense Scene. Hitchcock said that he will never let the bomb go off in a "suspense scene", because the audience gets worked up. If the bomb is going to get exploded, then Hitchcock won't shoot the scene in "suspense".