Continuity mistake: There is a shot of the beans in Jack's hand when the monk gives them to him. There are a total of 8 beans. Later, one of the beans goes under the floorboards of Jack's house and that turns into a beanstalk, bringing the bean count down to 7. After climbing the beanstalk, Roderick forces Jack to give him the beans. Jack keeps one of the beans bringing the bean count down to 6. No more beans are used after this until the giants use the beans as a way down to Earth. But when the lead giant takes the beans out of the bag, there are now only 5 beans.
Continuity mistake: When Elmont is put on the cream and flour before the giant bakes him, his back is smeared with cream, but when he escapes his back is clean.
Continuity mistake: When the humans and giants are pulling the ropes to open and close the gate, the hooks of the big guys disappear in one moment of the struggle.
Continuity mistake: When Jack and the princess are going down and see the lights on the ground from upside down, the distance between them and the lights changes between shots.
Visible crew/equipment: In the scene where Jack is running through the forest following the giants to their lair, we can see the tracks of the camera dolly under the leaves on the ground.