Continuity mistake: When Fairy Godmother is throwing the books behind her, the book "Snow White" lands on the other books. "Snow White" noticeably changes position between two shots. (00:41:15)
Trivia: In the Fairy Godmother's workshop when Shrek dumps the cauldron of potion over the employees, two of them are transformed into Lumierre and Cogsworth from "Beauty and the Beast" (1991).
Continuity mistake: When Puss in Boots plants his sword in the ground then jumps out of his boots, his sword, boots and hat are nowhere near any trees or grass. Yet after attacking Shrek, Puss in Boots lands in his boots, and his boots, sword and hat have moved to being right beside a tree. (00:32:30)
Continuity mistake: When Shrek and everyone else are trying to get into the castle, shots of Shrek facing back toward the other side of the drawbridge are missing the others, i.e. the pigs, Wolf, Donkey, Puss, Pinocchio, and mice. (01:13:55)
Continuity mistake: When the door to Shrek's house is first opened (just after the honeymoon), it opens into the house. Every other time it opens to the outside. It's not a two-way door, because you can hear it hit the doorframe. (00:04:50)
Continuity mistake: When Shrek first meets Puss In Boots, Puss In Boots bursts out of Shrek's clothes "Alien" style leaving a tear. Then when we see them enter the Fairy Godmother's factory the tear is gone for the rest of the movie. (00:32:35 - 00:38:30)
Continuity mistake: When Fiona shows her fighting talent by saving Shrek, they approach the trap holding hands, yet Fiona is not even visible in the medium range shot when Shrek is caught. (00:03:55)
Continuity mistake: During the first night in the castle, Shrek walks to the door of their room and his ears wilt. In the following pan shot to the king's balcony, his ears are standing up again. There is no time in which he could have voluntarily changed them. (00:22:40)
Continuity mistake: When the request is made by the messenger to have Shrek and Fiona come to Far Far Away for the wedding party, as the trumpeteers troop off in the background you can see their footprints on the ground. However, when the same view is shown again seconds later the footprints are gone. (00:07:45)
Suggested correction: How is that a mistake? Lots of doors open both ways.
Doors that open both ways are called a double swinging door and use sprung hinges (or gravity) to bring it back to the center/closed position when not being pushed. It can go both ways because there is no stop casing for the door to hit against when closed (or frame is that is the design). We see Shrek's door hit a stop when slammed, and hear it hit the stop. Meaning there IS a stop, so it is impossible for the door to swing past it, meaning it is impossible to be a double swing, but we see it go in and out in different shots, which would be impossible.