The Secret of the Unicorn: Part 2 - S1-E4
Continuity mistake: Thomson shows Tintin that he has had an elastic band attached to the wallet in his pocket as an attempt to catch the pickpocket. When they first use, the wallet with the elastic band is in Thomson's right pocket. In the next scene, when the pickpocket attempts to steal Thomson's wallet, it is now inside his left pocket. (00:30:20)