Cigars of the Pharaoh: Part 2 - S1-E7
Plot hole: The doctor at the mental hospital reads the letter Doctor Finney wrote him. It read that it was Tintin who was insane and Doctor Sarcophagus who wasn't insane. However, although he totally bought it, he never even took into account that Doctor Sarcophagus was pant-less or the fact that he was dancing like an Egyptian guy, which would have been enough to prove that Sarcophagus was the insane one. (00:33:15 - 00:34:00)
Chosen answer: It is a pill that makes alcohol taste disgusting.