The bat used on set was a combination of a mechanical bat, animated bat, and live bat.
When Joss Whedon found out the script for the episode involved a bat and a joke about Jim turning into a vampire, he was initially surprised by the idea and assumed the writing staff was playing a joke on him. But they insisted that his directing this particular episode was completely random.
Joss Whedon directed this episode with a subplot involving Jim transforming into a vampire. Whedon also created Buffy the Vampire Slayer (1997). His vamp mythology is borrowed heavily in this episode.
Pam's painting that Michael hangs on the wall in the office remains there until the end of the series.
It is in this episode that Meredith contracts rabies when Dwight puts a bag over her head to trap the bat.