Tintin and the Picaros: Part 2 - S2-E9
Revealing mistake: When Haddock walks in view of the helicopter pilot, it cuts to an interior shot of the helicopter where the pilot says "What's that? A Picaro by the river?" A couple of shots after this, there is another interior shot of the helicopter where the pilot then says "Caramba. He's disappeared." In both of the two interior shots, it is noticeable that the same footage has been used in both the shots as the exact same land is outside the helicopter is in both of the shots. The only difference in the second shot is that Haddock has been removed. (00:26:20)
Chosen answer: It is a pill that makes alcohol taste disgusting.