Chokolade
It strikes me that the film includes some handy hints on how to spot enemy agents - suspicious behaviour, the use of 'continental' numbers and so on, as one might expect from a propaganda film.
But - I find it hard to believe that the Germans would really be stupid enough to equip their agents with bars of chocolate which had 'Chokolade' emblazoned on them in large, gothic type. Bit of a giveaway, no? For me, it's the only bit of the film which is seriously lacking in credibility.