When Veronica (Kristen Bell) goes undercover at the Pastor's office and says she's pregnant she uses the name Hester. Hester Prynne is the main character of The Scarlet Letter (1995). She is shunned for having an affair and becoming pregnant.
Veronica's (Kristen Bell) comment that witnessing Madison's (Amanda Noret) birthday has reminded her to get a birthday gift for Mac (Tina Majorino) is a callback to episode 1.11 Silence of the Lamb (2005). In that episode, Veronica discovered that after Madison and Mac were born only days apart in the same hospital, they were accidentally switched and sent home with the other's parents.
The promo for this episode was edited together to mislead the audience that Veronica (Kristen Bell) was pregnant.
Veronica (Kristen Bell) finds out the time of O'Dell's (Ed Begley Jr.) murder after a witness says he watched Space Ghost Coast to Coast (1993) at 2:30am. The episode title is Explode (1996), and is the 20th episode. It was also written by Rob Thomas.
Even though we don't get a close look at Madison's mother (Amanda Noret), we can clearly see that it's not the same mother we met in 1.11 Silence of the Lamb (2005).