The advice given by the butler, Antoine (Pedro de Cordoba), to his soldier son concerns having rhubarb pills available. Rhubarb was used primarily for digestive complaints including constipation and diarrhea which were among major complaints by WWI survivors, Antoine having served in the Great War.
Chan's prescient aphorism at the film's conclusion, expressing pessimism about the upcoming Munich conference was filmed months prior to the start of World War II.
The twenty-third of forty-seven Charlie Chan movies.
The plane crash is footage of a crash that occurred on 9/2/33 at Floyd Bennett Field in NY. The aviator, Francesco de Pineda, was attempting to fly nonstop from NY to Baghdad. His overloaded plane never got airborne and crashed. The footage is still available on YouTube.
The aircraft show loading for departure at the end of the movie is a Bellanca CH-400 Skyrocket with what may be a replacement rudder. This plane was apparently chosen to match the film of the aircraft crash of Francesco de Pineda on 9/2/33 at Floyd Bennett Field in NY, used at the climax.