Bill Murray has said during interviews that he hates that he didn't think to have Garfield say his famous Ghostbusters (1984) line "Dogs and cats living together... mass hysteria!" (in the scenes of Odie being introduced to the house) until after all post-production had been completed, and it was too late to add it.
Bill Murray named this movie and Garfield: A Tail of Two Kitties (2006) as one of his regrets in Zombieland (2009).
In an interview, Bill Murray stated that he originally thought the script was written by Joel Coen of the Coen Brothers. It wasn't until the recording process, and watching dailies, that he realized that it was written by Joel Cohen, not the same person of whom he was thinking.
According to an article in Premiere Magazine, much of Bill Murray's recording sessions were done aboard the boat he was occupying while filming The Life Aquatic with Steve Zissou (2004) in Italy. Apparently, Murray wasn't impressed with the recordings he did while on land.