If you are tense the effect of strain is conveyed much better this way than by giving an impression that you can do what you like with the bars anyhow. As the bars crash, stand up in a straight line shoulder to shoulder for two or three seconds before going off. But do be careful to rehearse this sufficiently so that the bars don't topple down when you let one hand go. AII through the sketch, which is quite short, the main things are tempo and emotional intensity. Remember your two media are words and faces.
Facial expression is just as important as the words.
While one prisoner is speaking, the others must be acting alt the time reflecting the words. Tense, haggard, anxious, determined and other expressions suggest themselves, as the limes progress. Feel the sketch, mean it, and you will convey the message of it in a way that will strike home to class-consciousness that is latent in even the most reactionary member of your worker audience.