An audience member has accused the Blue Man Group of forcing a camera down his throat during a performance in Chicago.

James Srodon, who was watching the popular show with his 8-year-old grandson, said he was an unwilling participant in the stunt in October 2006.

The group consists of a trio of mute actors covered in blue paint, whose shows traditionally feature a large amount of audience involvement.

Srodon, from California, is suing the act after allegedly suffering nose bleeds, loss of fillings and nightmares following the performance at the Briar Street Theatre.

In the lawsuit filed in Cook County Circuit Court, he said the men held his neck and arms and forced his head back to insert an "esophagus cam", before an image of his mouth and throat appeared on a screen on the stage.

He said: "When I started struggling, it seemed like this fellow, he tried to be more aggressive with this device and shoved it way down my throat."

He added: "I want other people to know about this. I was a guy who wanted to take his grandson out for a fun afternoon."

The group's Chicago general manager Kori Prior denied that the stunt had been real, saying: "An actor holds a camera to an audience member's mouth, doesn't enter their mouth, and then we play a video. We have been performing this show in this theatre for 10 years and have never had this issue before."