The Castafiore Emerald: Part 1 - S3-E7
Revealing mistake: When Castafiore is showing everyone the Castafiore emerald, after she says "He named it in my honour", the shot cuts to a close-up of her hand, saying "The Castafiore Emerald." At the start of the shot, she has two rings on two fingers, then she turns her hand and the two rings vanish from her fingers entirely. (00:09:00)
The Castafiore Emerald: Part 1 - S3-E7
Continuity mistake: After Haddock tells the gypsies that they can camp near Marlinspike Hall, Tintin and Haddock return to the manor. As they walk up the stairs, Haddock has his cane in his left hand, but when they walk through the door, Haddock suddenly has his cane in his right hand. (00:03:35)
The Castafiore Emerald: Part 1 - S3-E7
Revealing mistake: When Castafiore locks her jewels in the drawer, she places the key inside the lock, but the key visibly surpasses the edge of the lock. (00:10:00)
Chosen answer: It is a pill that makes alcohol taste disgusting.