Continuity mistake: In the scene immediately following Fiona's thrashing of Robin Hood and his Merry Men, Shrek is holding Donkey and they are staring at Fiona in disbelief. When Shrek drops Donkey and turns to follow Fiona, you can see his entire backside and it's unpierced. In the next scene, Fiona discovers an arrow in his rump that wasn't there before.
Other mistake: Lord Farquaad wants to marry a princess to become a real king. The mirror shows him three princesses to choose from: Cinderella, Snow White and Fiona. But Cinderella wasn't born a princess! In fact, her only chance to become a princess was to marry a prince.
Continuity mistake: Sometimes Shrek's front door opens outwards, at other times inwards, yet it can't be "two-way" because whenever it closes, it slams against the frame.
Continuity mistake: At the start of the film, Shrek is painting his "Ogre Beware" sign, you will notice that quite a bit of the top left corner of the board is missing. When he hangs the board on the post it is the opposite corner that is gone. He did not paint on both sides.
Continuity mistake: The dragon flies down without a chain, then there is a chain dangling for Shrek to climb about to go to the castle, and while the dragon is flying, the chain is gone again.
Continuity mistake: In the scene where Donkey and Shrek are crossing the bridge to rescue the princess, Donkey trips and breaks a board. In subsequent shots sometimes you can see a little bit still stuck in the ropes, and sometimes it disappears.
Continuity mistake: At the end of the film, the three blind mice are turned into the horses for the onion carriage but a second later they are dancing on the piano.
Deliberate mistake: When a glass of milk is poured, if you look closely, the glass is filled but the level of milk in the bottle doesn't seem to lower.
Continuity mistake: In the scene where Shrek and Donkey are on the wooden bridge, when Shrek starts rocking the bridge, we see that the castle is still quite a way off. However, Donkey only takes a few steps to get to the end.
Revealing mistake: When Shrek and Donkey are sitting by the fire and looking at the stars, when Donkey asks Shrek about "our swamp" and Shrek says "We?" When Shrek blinks, his eyeball is slicing through his upper lid.
Continuity mistake: In the scene where Farquaad's men are chasing after Donkey and run into Shrek, their leader is holding a scroll. In the next shot, it completely disappears without him moving it at all.
Continuity mistake: When they are dining the second time, Shrek accidentally drops a cooked mouse, but when they stand up, the mouse is not there.
Continuity mistake: During the scene where Fiona pulls the arrow out of Shrek, Donkey faints. When he hits the ground about 6 leaves float up from the ground as if Donkey had fallen into a pile of leaves. When we next see Donkey laying on the ground and when Shrek picks him up, there are no leaves on the ground, they disappeared.
Factual error: As Shrek is sitting near the sunflowers field and staring at the Duloc (and day becomes night), we don't see the cathedral anywhere. It should be visible as such a big building, due to how big it is seen later, it should be very distinct over the houses' roofs.
Continuity mistake: In the scene where Shrek falls through the roof of the castle, in the shots where Fiona is in the background you can see the flower pot is on a table next to the pillow on the bed. However when Fiona reaches to get the flowers she reached down to the floor and not back towards the table with the flowers on.
Continuity mistake: When Shrek and the prince are talking about the swamp after Shrek has just beaten all of his knights, the flags move across the wall between shots.
Continuity mistake: When the magic mirror is brought in, we see the chain and hook that it is supposed to go on. Yet after the mirror is hung up, we pan around from the back of the mirror to the front and it appears that the chain has been attached to the back plate of the mirror. Where did the hook go?
Continuity mistake: When Shrek walks out of his house and finds the fairytale creatures, you can see the three fairies go into one of the tents that were set up. The shot goes back to Shrek for a minute and then goes back towards the crowd and the fairies are back in the place that they were before.
Continuity mistake: In the scene where the mirror is brought in for Lord Farquaad, Gingerbread Man lies on a tray on the table. When the mirror is shown, and it cuts back to Lord Farquaad, the tray is moved to the other side of the table.
Continuity mistake: In the scene with Lord Farquaad and the Gingerbread Man, Farquaad crumples one of the Gingerbread Man's legs into dust, and some crumbs fall out of his hand. When he opens his hands again, there is no sign of any crumbs. The only way that this is possible is for every last bit of gingerbread to fall out of his clenched fist.
Continuity mistake: When Fiona tears a piece of bark off a tree to make a door for the cave, the shape of the bark is different from the bare spot on the tree.