The Crab with the Golden Claws: Part 1 - S1-E1
Continuity mistake: The pilot of the seaplane has a mustache, and goes back to the site of the boat to see if Tintin and Haddock really are dead. When Snowy appears behind him and the pilot says "Where did you come from?", the mustache has vanished completely. Then as Tintin pulls on the pilot's leg, the mustache reappears again. (00:20:35)