Harpo Does Something Funny The legendary scene with Ty and Carl in Ty's "home" was added to the script solely because the writers realized that there wasn't a single scene in the movie that featured Bill Murray and Chevy Chase together and was almost entirely improvised.
Throw It In: A good deal of Bill Murray's dialog was improvised on the set, including his now-classic sportscaster monologue.
"It's in the hole! It's in the hole!"
What Could Have Been: Harold Ramis has said that he was told that Rodney Dangerfield was interested in doing the second movie. Dangerfield actually was attached, but was displeased with the script (as many turned out to be). With no suitable rewrites, he backed out.
Also averted. The filmmakers seemed to be asking themselves this when they realized that Bill Murray and Chevy Chase didn't have a scene together. Thankfully, they made one up pretty quickly.