Land of Black Gold: Part 2 - S2-E11
Revealing mistake: The Emir is always shown wearing a black robe with a yellow stripe down each sleeve. When the Emir is telling Tintin it was Bab El Ehr who kidnapped his son, there is a portion of the yellow strip next to the cane he is holding around his elbow, that keeps flickering from yellow to black and back to yellow again. This occurs three times in one shot. (00:27:15)
Land of Black Gold: Part 2 - S2-E11
Revealing mistake: When Tintin asks where he can find Mueller, the scene cuts to him walking through a market. Whilst he is walking through the market, he is wearing shades and the sun is reflected in them, but the reflection never stays still. The reflection is constantly flickering around the shades. (00:29:35)
Land of Black Gold: Part 2 - S2-E11
Revealing mistake: When Tintin and Oliviera da Figueria are talking with the guard at the castle door, the guard sneezes and Oliviera takes out a handkerchief saying "Some beautiful handkerchiefs." When Oliviera finishes taking out the handkerchief, as he says "Some", a weird mark appears on the screen, right where the handkerchief is located. This is visible for only one frame but it can still be noticed. (00:32:00)
Chosen answer: It is a pill that makes alcohol taste disgusting.