Alan Rickman may be happy playing opposite Helen Mirren in the Royal National Theatre's upcoming production of Antony and Cleopatra, but one co-star isn't - the asp whose bite sends Cleopatra to her grave.

The foot-long snake - nicknamed Cedric - has twice broken free from his box in the National's backstage. The first time, he was spotted by a cleaner and re-captured. But he has now been missing for a week since his latest escape last Thursday.

RNT staff suspect foul play surrounding Cedric's recent disappearance. 'We think someone might have stolen him,' RNT spokeswoman Fiona Walsh told What's On Stage, explaining that the container holding Cedric was very secure.

The RNT has stressed that the snake is non-venomous and completely harmless. Nevertheless, signs have been put up and announcements made at the theatre asking people to keep an eye out for it. 'There was one brief sighting yesterday so we think he's still in the building,' says Walsh.

The play's dramatic climax is not in danger, despite Cedric's reluctance. There have always been two snakes and the other, nicknamed Indigo, will play the part of the asp. 'Cedric was the understudy snake anyway,' says Walsh. If he doesn't turn up, the RNT does plan to recruit another understudy.

Antony and Cleopatra opens at the RNT's Olivier Theatre on 20 October 1998.