The Broken Ear: Part 2 - S2-E3
Other mistake: The chess pieces Tintin and General Alcazar use during their game are all white. There are never any black pieces at all. (00:29:15)
The Broken Ear: Part 1 - S2-E2
Other mistake: The villains lower a rope with a noose in it. They place it over a man's beard they believe to be Tintin. The noose is not tight yet, but it suddenly is when they pull on the man's beard, with no way for them to tighten it. (00:17:45)
Other mistake: As Professor Fossil is on the radio, there is a shot showing us him on a newspaper. Look at the words on the article. All the words on the article are fading away. (00:08:40)
Chosen answer: It is a pill that makes alcohol taste disgusting.