When Matt is trying to entertain Lizzie with magic tricks at the beginning, he picks up a black cloth from the table. In the next shot it is back on the table and then back in his hands in the next.
When Matt handcuffs himself to Lizzie and they become stuck, Matt is wearing his magician's hat and cape. Then when they begin to look for the key the cape and hat are no longer on him, but then a few shots later he is wearing them again.
During the montage of Lizzie and Matt at the charity drive golf tournament, there is one part where Lizzie is standing outside the Men's toilet as Matt uses it. However they are handcuffed together with cuffs that have a chain which is about an inch long, so there is no way Matt could use the toilet with Lizzie standing outside the door.
When Kate opens the can of nuts that Matt gives her, when the joke snakes spring out of it she falls into the pond behind her. You can clearly see that it is a double taking the stunt.
When Miranda hands Lizzie the drink as she stands next to the photo booth, you can clearly see and hear that the cup is empty, as you can hear ice rattle at the bottom; yet Lizzie sips as if there is liquid in it.
As Matt is annoying Lizzie with the magic trick involving the golden 'floating' ball, huge set lights and equipment are reflected in the balls shiny surface.