When Peter finds the old newspaper clippings in the back of Mary's doll, the headlines say "Hundreds Missing and Dead in Gates Falls Mill fire", and under it is the information on the fire. When Sally and Hook save Mary and the headlines change to "Mill Owner, Foreman Arrested in Arson Plot", underneath is the very same information that was on the last newspaper, which was supposed to no longer exist.
When Dr. Hook gives Otto a soda, the can is closed. The next shot reveals that the can is open, but later in the scene you hear Otto open the can.
In the episode "Seizure Day" when Brenda is making the potion for Stegman, as the camera zooms in you can see the camera's red light and someone behind it reflecting off a box just up from the red toolbox.