The Adventure of the Egyptian Tomb - S5-E1
Factual error: In the scene after Poirot pretends to be poisoned, a person folds the modern flag of the Arab Republic of Egypt instead the flag of the Kingdom of Egypt as it was at that time.
The Underdog - S5-E2
Factual error: Lily looks over part of the procedure for the manufacture of Astroprene. There are several problems with the chemical structures shown in step two of the procedure. This step appears to be a simple acid catalyzed rearrangement of the molecule shown. The procedure should begin with a C inside the hexagonal ring and end with the C outside the ring with no other changes. The errors include, among other things, a carbon atom at the lower left of the ring with two lines (bonds) to it. The C should have four bonds (lines), the two shown plus two to hydrogen atoms (H). The bonds to H may be condensed so the C will look something like -CH2 - (the 2 would be a subscript). (00:10:30)
Factual error: Poirot smells and very carefully tastes a drink and says, "Potassium cyanide." It is impossible to distinguish between potassium cyanide and sodium cyanide (the other common cyanide) by this method. In addition, there are another less common cyanides that would smell and taste the same as potassium cyanide. (00:16:01)
