The author does diverge from humor in spots, particularly in the second book, in which he makes observations about the German people that underline all the features that gave rise to the Nazi era, though notably, the author acknowledges getting swept up in pugilistic mob thinking himself
Poor mental development - Even in later years, children of mothers who smoked during pregnancy tend to be slightly shorter and have more difficulty with reading, mathematics, and related skills
Native peoples believed that bringing all of the elements together could invite balance and harmony
It was never used again, though Poirot did use a similar one in the adaptation of 'He was carefully engaged in brushing his coat before putting it on, and seemed wholly engrossed in the task.' (...) He opened a drawer, and took out a small dispatch-case, then turned to me.' (p