In Prince Charming's Big Show in Far Far Away, the number of shadows cast by players on the stage varies. Sometimes there is one shadow per player. Sometimes more.
When Shrek and Artie are captured by Charming, and Shrek insults Artie to save his life, Artie leaves and, in a following shot, is seen walking away some distance from the castle. However, when Puss, Donkey and the other fairytale characters bump into him later, he is back by the castle gates.
When the women escape and prepare to "take care of business", we clearly see when Snow White rips off her sleeves that she has a heart shaped tattoo with "Dopey" written on it on her right shoulder. Later, when she summons the critters to attack the tree guards, her right shoulder is bare.
Fiona and the other women launch their attack on the city of Far Far Away. Ugly Sister punches a guard. From behind, her punch is delivered with the left hand. Then when viewed from the front, she follows through with her right hand.
At the end of the film, when Merlin puts Puss and Donkey back in their correct bodies, they turn side on to the camera and hug - no tails can be seen.
When the ship crashes into the rocks, debris can seen flying back. In fact the debris should fly forwards due to the forward motion of the boat. This is the basic principle of Newton's 1st law of motion.
When puss , donkey and the others come into Shrek and Fiona's room , and start talking about the day's activities , Shrek gets back in bed and turns on his side before covering up with a blanket , when donkey yanks the covers off , Shrek is suddenly lying on his back .
Merlin accompanies the piano player to play four-handed at his left side. The part Merlin plays is high-pitched. To play high notes, you should sit at the right side of the piano.
At the end of Shrek 2 (2004) when Donkey discovers he has babies there are six of them. Yet in Shrek the Third (2007), there are only five babies.
After Shrek asks how his becoming a father could happen, Donkey asks Puss In Boots "How DOES it happen?". Being a father of five children himself, Donkey should know full well how it happens.
When Prince Charming met Arthur, he told him that his name is actually Artie. However, Artie was actually his nickname, not his real name.
Merlin claims his rocks to be organic, but rocks cannot be organic.
While King Harold was talking to Shrek, he told him that he was proud to call him his son. But since Shrek was Fiona's husband, he should've said "son-in-law".