Who said cartoon characters can’t make a mistake? We have the proof to show they can and they have. This proof comes in the form of a Thanksgiving song that Linda Belcher sings to her husband Bob on Bob’s Burgers. That holiday song, nor any song, was ever written in the original script.
Linda’s voice actor John Roberts just decided one day he wanted to burst into song. Not only did the cast find it entertaining, so did the writers who kept it in the show, and the viewers, once they saw the episode the day it aired. That improvised song ended up becoming a huge hit.