Corpsing is British theatrical slang for unintentionally breaking character by laughing. In North American TV and film, this is commonly referred to as breaking, and it is generally categorized as a blooper. The origin of the term corpsing itself is unclear, but may come from (provoking an actor into) breaking character by laughing while portraying a corpse. As the name suggests, many examples of corpsing have been created from actors performing this role or related roles, such as a sleeping or unconscious character.
A significant aspect of the phenomenon is the frequently deliberate and usually benign attempts among actors to cause this in cast members. During the "Pete and Dud" sketches in the BBC comedy series Not Only... But Also, Peter Cook would deliberately ad lib in an attempt to make Dudley Moore corpse—and he invariably succeeded.
Corpsing is not exclusive to the theatre. One of the most famous examples of this is on the cricket programme Test Match Special, in the famous "leg-over" incident.
In the final scene of the Fawlty Towers episode "Gourmet Night," when Basil (John Cleese) delves into the trifle with his hands and pulls it apart, actress Prunella Scales, who plays his wife Sybil, can clearly be seen in the background trying to suppress her laughter.
One of the most famous American examples of comedy partners trying to "corpse" is between Tim Conway and Harvey Korman during The Carol Burnett Show. Similarly, during production of Mork and Mindy, Pam Dawber often found it impossible to maintain the proper composure in character at the sight of co-star Robin Williams's antic comic improvisations during filming, and her amused reaction is visible on aired episodes. Mindy Cohn, of The Facts of Life fame, also had trouble keeping a straight face during scenes and can be seen smiling as if she was quite amused throughout the series's run. In an episode of Friends that has Phoebe (Lisa Kudrow) screeching along with a bagpipe, castmate Jennifer Aniston can be seen clearly breaking into laughter in the background. The Saturday Night Live sketches featuring Debbie Downer (Rachel Dratch) are also notable for corpsing. Jimmy Fallon is also known for breaking character by laughing on Saturday Night Live.