In the first shot, Annie asks Britta "didn't they say 304?" at the door of Troy and Abed's apartment (No. 303) and Britta responds "No, 303, I wrote it down twice".
This is a reference to the fact that this episode was shot as the third of the season and planned to air as 3x03 but was later changed to 3x04. Gilian Jacobs wrote the joke after the change was made.