Chris Cooper suffered a bout of nerves during a prison visit to research his character for THE TOWN - he "freaked out" when he realised he was mixing with serious offenders.
The actor plays a convict in Ben Affleck's acclaimed crime thriller and many of his scenes were shot in a real life jail.
Cooper visited the prison with his co-star Jeremy Renner before filming began, and admits he felt uncomfortable throughout the day.
He tells the New York Post, "I was nervous going into that prison. Everyone behaved. Kept their distance. Prisoners were ordered to march past hugging the wall. The place is colour-coded. Five grades of colour. Different uniforms for different crimes. The most serious offenders wear red.
"Guards took me to their boards, which show the inmates' photos in groups - skinheads, rapists. I freaked out afterward for hours. I'm out in sunny California, and those guys are still there. We had one day to shoot in jail. I went for a day's visit a month beforehand to meet the guards and warden. I spent five hours soaking up the atmosphere with Jeremy Renner. With no division between us and the prisoners, we got a real close look."