The Lethal Eagle Affair - S1-E11
Revealing mistake: Mark hides inside the grand piano - improbable (there's not enough room) unless the piano is a mock-up without any real harp or strings. And in fact, when he jumps out, you can see that there's nothing inside. Somehow, though, the piano still makes sounds when Dieter touches the keys. (00:27:00)
The Lethal Eagle Affair - S1-E11
Revealing mistake: While Madame Gita is testing the death ray device, she orders Franz to go check the power. He trots off to obey, and in the process crosses, miraculously unscathed, directly in front of the "deadly" light beam. (00:42:15)