What does an actor do when they are 'corpsing' on stage?

"Corpsing" is British theatrical word used 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.

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.