In one scene where Rob and Nick are talking over pizza and beer, the pizza slices in the box change positions a couple of times.
In the beginning of the movie when she is being interrogated her hands change positions constantly and the piece of pink paper goes from her hands to laying on the countertop.
When Holly and the elf girl she's replacing are in the same room, it's obvious they are two different sizes and Holly would never be able to fit in the tiny elf costume, yet when she comes out it fits her perfectly.