El cangrejo de las pinzas de oro
Harry Thompson stated that the "overriding theme" of "The Seven Crystal Balls" was "fear of the unknown", adding that while it did blend humour with menace, it remained "Hergé's most frightening book". He noted that the story marks the complete transition of Captain Haddock from the "pitiable drunk" which he was introduced as in "The Crab with the Golden Claws" to the position of "chief sidekick and comic attraction", with Snowy being relegated to the position of "normal dog".