15% of Dumb and Dumber
If a movie stars Jim Carrey, you can bet that there are quite a few ad-libbed lines and blooper scenes that make the final cut. According to one of the co-directors, Peter Farrelly, roughly 15% of the entire movie relied on Jim’s unparalleled improv and comedic skills.
While shooting Dumb and Dumber, the Farrelly brothers had the actors play scenes out twice. For the first takes, they would follow the script through-and-through. For the second takes, they let Jim and Jeff Daniels improvise their lines. In the end, they wound up keeping a huge chunk of their improvised scenes, such as the most annoying sound in the world and the Big Gulp line (to two strangers who wandered onto the set).