McCallum on the train: cool under pressure or flubbed line?

OK, so British airmen are on the train, escaping thru German territory, in the middle of a lot of Germans. Not only do they have to answer questions in German, but to do so with a convincing accent. The scene where the Gestapo guys are going thru the train, randomly asking for papers & questioning people, I observed this: 1 of the Gestapo asks David McCallum why he's travelling? He says "fur meine..." and then a full 3 seconds goes by, and he starts over, says "fur meine geschaft [for my business]". It looked to me like the actor simply had trouble memorizing them 3 words - and if his character's a native German, wouldn't that odd speech characteristic tip off the Gestapo guy? The other possibility is that he's playing it cool - he's a German on legitimate business, so he's so nonchalant he even talks...breezy. Does any1 else who saw this scene see this, and what do u think?