Just before the breakout, the prison guard is shown walking the corridor with a ring of keys in his right hand. After he gets knocked out, the key ring is in his left hand, closer to the cell.
Whitey shows Slip a newspaper story about a chemical plant robbery. The first paragraph has details about said robbery, but the second paragraph of the article relates to a peace conference.
When Slip and Satch first arrive at their prison cell door, a shadow of the boom microphone can be seen moving on the wall above and forward of the prison guard.