Mr. Tweedy's shotgun disappears on the porch in the opening sequence.
The chicken catapult changes during Mac's demonstration. The teeth on the cog and ratchet point in different directions within the same scene.
The "Egg Production Table" in Mrs. Tweedy's hand changes twice.
The tire mark on Mrs. Tweedy's forehead disappears/reappears between shots.
In the overhead shot of the huts when Rocky starts teaching the chickens how to fly, hut 24 is behind hut 23. Later, when Nick and Fetcher are watching them jumping on the hot water bottle, huts 23 and 24 are next to each other.
Bunty claims to have laid five eggs in one morning, and is seen again later producing multiple eggs at once. In real life, chickens produce exactly one egg each day.
Chickens aren't completely incapable of flight as the movie would imply. Their body structure simply doesn't allow them to maintain altitude for very long. With that said, it would still be impossible for chickens to fly over a ten-foot-tall fence.
While Nick's use of "Voilà!" is correct and French, his later line to Rocky of "El merchandiso", is not Spanish as Fetcher says it is. In Spanish, "the merchandise" (as he wanted to say) would actually be "la mercancía". Then again, it may be justified as Nick doesn't seem like the sort of character to know that.
The chickens are visibly seen to have teeth in their beaks. Real chickens don't have teeth. However, having teeth serve as part of the character designs as the chickens are not realistic.
After Mrs Tweedy falls off the plane, the shot of Fowler saying "The old bird bought it!" is flipped (the "17" is the wrong way round and is also on the wrong side of the hut door).
When Mac shouts 'We're giving 'er all she's got!' the crank motor on Fowler's right and the wing it's connected to briefly move out of sequence with each other.
Closed captioning mistakes (American English):
"Keep peddling" instead of "keep pedaling" "I didn't do owt" instead of "I didn't do ought" (as in "nothing")
"Keep peddling" instead of "keep pedaling" "I didn't do owt" instead of "I didn't do ought" (as in "nothing")
During the film, Rocky is cycling through the English countryside listening to a radio. On the radio is 'The Wanderer' by Dion. The film is set in 1959, but 'The Wanderer' was a UK hit in 1962.
When Ginger and Rocky are in the chicken pie machine, he makes a reference from The Simpons about the dough. He says "D'oh ! Get it ? Dough !" Which doesn't make sense because the film is supposed to take place in 1960s. While the first episode of the show aired in 1989.
In the last few minutes of the movie, when Rocky comes back to the farm on his tricycle, he is heard yelling "Ginger!," but if you took a good look at his beak when you hear him say it, you will find that the beak is not opened. It's closed.
Puppets were often mounted to rigs so they could be suspended in the air. The rigs were edited out of each frame after filming, but there is a short cut in Chicken Run where a rig was missed:
Inside the pie machine when Rocky is falling out of the meat chute, the 17-frame cut of him falling directly into the camera still has the puppet rig visible.
In the first scene with the rats, when Ginger is leading the rats around the corner with her lantern, two wires that provide current to the lantern can be seen trailing off the puppet's back. At the same time, a lighting instrument can be seen on the floor, just on the edge of the frame, which may be cropped out on some displays.
Mac tells Rocky that "You sprained your anterior tendon connecting your radius to your humerus." However, tendons connect muscles to bones and the radius and humerus are both bones, so she should've said 'ligament', not 'tendon'.