Stu's hands, which were covered in cake, are totally clean in the next scene, when he jumps away from the dog.
When Stu wakes from the coma, his hands are outstretched in the shot of Julie. When we pan back to Stu, he reaches out and says, "Whoa baby."
When Stu awakes in the operating room as the gymnast, the large digital clock behind him reads 20:03:18. This could not possibly be the time as the banquet begins at 6pm. We even see a shot of a clock in Stu's studio reading 5:45pm.
When Monkeybone is singing as Marilyn Monroe and takes off the dress, he is wearing a suit. But in the next shot he is just wearing his vest.
When the Gymnast flips from the first bar to the second in order to get into the party, you can see grip powder on the second bar from previous takes.
When Stu is singing in the club to Julie, as he passes a table a boom shadow is visible across his face.
As Stu is transferred into his gymnast/organ donor body, when the doctors are pulling out organs, he stands up and startled the doctors. Just then, there is a boom mice visible about the doctors.
Chris Kattan is in very poor shape for a gymnast.