Two bad-guy Nazi guards with guns return to the entry room of a mill where Banks, Cole and the Scotland Yard detective/butler are being held in the inner room. Check. It's all over for these two Nazi agents. The handwriting is on the mill wall. Militia is outside, surrounding them, shooting through the windows. The baddies' gun ammunition is likely low, as they've been shooting a lot. I didn't notice they brought extra rounds. Check.
Problem solving is no longer necessary for our hostage three. They clearly heard the rescuing ruckus. All they have to do is bide their time and enjoy their rescue. They don't have to bother to fulfill any escape plan.
But no, here comes their superfluous special effect. A large, heavy millstone is lever-ready to come crashing through the door connecting the inner room to the mill entry. Only it's narrower than about a third of a man's body, and quite unlikely to remain upright for more than a foot length of travel if levered and pushed. Makes you wonder how this point was staged in the play format this film was based on.
Now if you were a Nazi/bad guy, would you stand around huddled next to your pal in perfect line with the approaching stone, or would you have good enough reflexes to just hop aside? A second or two of warning is all you'd need to get out of the way, as the stone improbably lumbers along its slow, inexplicably upright gravitational path. The baddies stare at it and get in line for the impact.
Well this film still gets 9 stars from me out of 10, mainly for the entertaining interplay between comedy and intrigue, and for the excellent cast and script, and overall sweetness, despite credulity-bending here and there. Enjoyable movie for a rainy afternoon.