When unlocking the rooftop door the guard uses an old fashioned mortise key, but Briggs locks it outside with a modern cylinder key.
During the staged "trapeze accident," Barney has released one side of the trapeze bar support, leaving Crystal hanging by a single rope with the other rope dangling below her. After she recovers and is being lowered, the trapeze has been rehung.
As Crystal (Mary Ann Mobley) is descending from her trapeze, her white ballet slippers have a white strap across them. But as soon as she's on the ground, the straps are gone from the shoes.
When Cinnamon and Crystal stage a fight to distract a guard while the escape is made, the "grass" upon which they fight is an obvious mat, evidenced by the large wrinkles that appear in the surface.
The man climbing down the wall of the prison is obviously a stunt double to Martin Landau.
When the team is leaving at the checkpoint, it's supposed to be night time. Yet the sky is light blue. Also the guard says he cannot hear the commandant because the calliope music is too loud, even though Barney is playing music far down the road. There is no way the commandant could hear the music that far down the road.
When the soldier flirts with Crystal near the beginning, there a poster for the "Leipziger Messe" is posted to an advertising pillar. Such a poster for a trade fair in Germany makes no real sense in Hungary.