Denzel Washington turned down a stuntman and insisted on shooting a tough waterboarding scene himself in new film Safe House.
The star plays a fugitive in the movie - with Ryan Reynolds playing a young CIA agent tasked with looking after him - and in one scene is subjected to gruelling punishment.
Denzel, 57, told Vulture: "I wanted to see what it would be like... It's strange. You can't breathe in, because the water comes in, and it's filling up your mouth.
"And that was just one time for a short time.
"Imagine having that done for 20, 30 seconds? You will give up the answers! You may not necessarily tell the truth, but you will tell [your captors] whatever they want to hear."
Waterboarding is a form of interrogation where water is repeatedly poured over the victim's face.
Ryan added: "He went all out for this movie. I would definitely not like to be waterboarded. It was intense. Disturbing.
"I had sympathetic pain. I always get sympathetic pain. I wish I didn't. I felt like I was drowning."