The Seven Crystal Balls: Part 1 - S3-E3
Factual error: When Tintin and Haddock are watching the two clowns performing on stage, the clown of the left is shown stepping in a spilt puddle of water on the stage, but the water is never affected, even when he steps in it. The water just remains completely still and no water is ever shown dripping off the clown's shoe. (00:04:40)
Chosen answer: It is a pill that makes alcohol taste disgusting.