Revealing mistake: In the train scene when Mr. Bean plugs his ears with his socks you can see that he didn't use the ones he was actually wearing before. Once he took them off he placed them in front of him but reached slightly to his right for the ones he plugged in his ears. Also those where still flat like after ironing them and didn't look worn at all.
Revealing mistake: When the dog jumps up at the Postbox, it wobbles slightly, meaning that it's a prop and not a real Postbox.
Chosen answer: I'm guessing it is because he bought a new car. At the end of the first Bean, he crashed the mini. You hear the crash and see his wheel bouncing down the road. Safe to assume it was a write-off.
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