Dr. Kelso rolls down the hall and crashes after the Janitor attaches wheels to his shoes. But the first time, when he's out of control, the roller-skates he's actually wearing are visible.
In the final scene, creator Bill Lawrence can be seen behind Carla when she is talking to the janitor. However when it pans out to the whole staff, Bill Lawrence is laying down in the very front.
When Carla asks how many people won't be able to make it to the staff photo shoot everyone raises their hand, including the Todd. However, he is the only one besides Carla who appears in all of the three previous years' pictures that are shown, and he's ready and waiting on the bleachers when she lures everyone else into the parking lot for the new photo.