The famous scene that begins when Ty Webb's golf ball crashes into Carl Spackler's ramshackle house was not in the original script. It was added by director
Harold Ramis after realizing that two of his biggest stars,
Chevy Chase and
Bill Murray (who did not get along due to a feud dating back to their days on
Saturday Night Live), did not have a scene together. The three met for lunch and wrote the scene together. Although it has nothing to do with the plot, it is widely regarded as the funniest scene in the movie. This is the only time that Chase and Murray have appeared in a movie together.
Bill Murray filmed all of his scenes, including the famous scene with Chevy Chase, in six days. (Many people expected them to have another confrontation as they had had during Chase's return to Saturday Night Live years before. They were professional and didn't show any signs of their alleged previous feud.
hey man i heard ppl were hating on me over at roll it up
eh don't sweat it man, they just don't getcha
what? how could a bunch of stoners NOT get me? 
i'm cool
well I know that 
i don't get it
i know you don't chevy, it's ok man, you're rich and you got goldie hawn, score buddy 
oh yeah i guess you're right
i'm chevy chase and you're not
