Due to the emotional tone of the final scenes, the producers asked the network not to run commercials over the closing credits.
The ending shot with Homer gazing at the sky was decided at the table read, but the drawing at the end was inserted by David Silverman because it was felt that the scene was so touching that no other lines were needed. As a result, no promos were aired over the credits during the original airing of the episode.
Part of the fun of an episode about Homer's mother for the writers was that they were able to solve several little puzzles, such as where Lisa's intelligence came from.
When Mona hits her head while getting into the van, her voice is done by Pamela Hayden because Glenn Close could not say "d'oh!" properly and thus they used the original temp track recorded by Hayden.