A Bat is discovered residing in the ceiling of the Scranton office when Dwight identifies some animal stool that had fallen from a hole in one of the tiles in the episode "Business School".
When a bird crashed into the office's glass doors in "Grief Counseling", Pam said that "I think he just really, really wanted to come inside our building to spread his cheer and lift our spirits with a song.", but no one seems to consider that the same may be true of the Bat. Throughout the episode everyone tries to capture it but just end up shutting it in different rooms every time. It is let into the break room later in the episode and gets tangled in Meredith's hair. Dwight uses a garbage bag to remove it from her hair.