Continuity mistake: In the scene where Shrek is tangling the dragon's chain around the pillars, you notice that when Shrek crosses his own path, he jumps over the chain, but the dragon doesn't, so it would've been tripped over by the chain. And to make matters worse, when you see the camera focusing on Shrek, right before he tells Fiona and Donkey to head towards the exit, you can see the chain is high enough to run underneath without having to duck.
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.