Continuity mistake: When Carlotta brings the plates for the meal they all have a dome cover with a top handle, but when Sebastian runs across the table those handles have changed. (00:54:50)
Other mistake: When Nick is in the spoon, the milk around him turns green.
Revealing mistake: When they gather around to watch what happens when you put the slime in the toaster, you can see when the toaster starts popping that it has little pneumatic pistons attached to the bottom, making it jump. When the toaster gets picked up off the table you can view its power cord which is entirely too big - more likely air lines. (00:41:15)
Visible crew/equipment: As Rachel runs to the airplane through the line of passengers, on her way back to the house from her parents in Chicago, you can see lighting equipment reflected in the glass window, before it cuts away. (01:11:00)
Continuity mistake: When Redferne finds the page of the Grand Grimoire, he is holding it with his right hand. In the next shot, he is holding it with his left hand. (00:52:17)