Continuity mistake: At the start of the meeting, there are 7 people including Tintin. With the exception of Tintin, this makes 6 people. After Tintin finds out the identities of the brotherhood, there are 7 people with the exception of Tintin. Tintin did take someone's clothes, however all the people there are dressed in their robes and Tintin is dressed in the robes as well.
00:38:45 - 00:40:00Casual Person
Continuity mistake: When the first brotherhood member goes into the meeting room, only a wall is visible when he opens the door. When Tintin goes into the room disguised as a brotherhood member, a whole table, people and the emblem sign has appeared from nowhere.
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 - 00:34:00Casual Person
Continuity mistake: As the doctor and Tintin walk through the mental hospital, they stop at the first door on the corridor. After the doctor walks back the way he came, he hasn't walked past the door he locked Tintin in yet, indicating that it is now the second door on the corridor he locked Tintin in.
Continuity mistake: When Tintin and the doctor walk through the corridor to the room, the door to the room is white and the window on the door is closed. In the next shot, the door is a yellow/beige color and the window on the door is now open. The window is then closed after the doctor locks Tintin in the room.
Continuity mistake: In the scene where they find Mrs. Snowball fainting, Mr. Snowball (standing to her left) grabs her hand and Doctor Finney stands next to Mr. Snowball on his right. A few shots later, it is now Doctor Finney standing next to Mrs. Snowball on her left and Mr. Snowball next to Doctor Finney on his right. In the shot after that, Mr. Snowball is now standing next to Mrs. Snowball on her right.