Factual error: Tintin says they only have one bullet left. That bullet is in the magazine,and since it is a semi automatic, there should also be one in the chamber, meaning they would have two bullets. Even if they only had that paticular bullet, he doesn't cock the gun, meaning the chamber would be empty and therefore wouldn't fire.
Friso94
Plot hole: Tintin has a pretty sharp eye (as seen in his fight with Haddock, in the radio room, the Thompsons following them etc.), but he didn't notice that Sacharin's Unicorn was still fully intact? His own model was pretty badly damaged, with all sorts of wires hanging loose after its fall. (00:10:00 - 00:15:30)