Chicken Run

Mr. and Mrs. Tweedy run a failing chicken farm in Yorkshire; the chickens are caged in the style of a prison camp with a high fence and barbed wire, and two dogs patrol the grounds. Chickens that fail to produce enough eggs are slaughtered for food. Frustrated at the "minuscule profits" generated by the farm, Mrs. Tweedy comes up with the idea of converting their farm into full scale automated production.
One chicken, Ginger, has long had visions of escaping with the help of her hen friends Babs, Bunty, and Mac, and two black-marketer rats, Nick and Fetcher, who help to acquire "contraband" from the Tweedys to aid Ginger's plans. However, she is always caught and put into solitary confinement. While thinking of a new plan, Ginger witnesses a Rhode Island Red cockerel fly over the fence and crash into one of the coops, spraining his wing. Ginger and the other chickens help to hide him from the Tweedys and care for his wing, learning that his name is Rocky. Ginger is particularly interested in Rocky's ability to fly and begs him to help train her and the other chickens to do the same. Rocky is coy, but proceeds to try to help train the chickens, unable to fully demonstrate due to his broken wing. Meanwhile, strange boxes arrived containing the Tweedy's new machinery and the chicken's food ration is doubled to fatten them.
Amid the training, Rocky holds a large party to help relieve the stress, where it is revealed his wing is healed, and Ginger insists he show them how to fly the next day. The pie-making machine is finally working and Mr. Tweedy, who completes the assembly, immediately grabs Ginger for a test run. Rocky is able to save Ginger and helps to damage the machine, giving the chickens only a short time to plan to escape while Mr. Tweedy repairs it. When morning arrives, Ginger finds Rocky has fled, leaving behind a part of a poster that shows him to be a stunt cockerel, shot out of a cannon from a nearby circus and unable to fly by himself. Ginger and the other chickens are depressed. Fowler the cockerel tries to cheer the hens up by telling tales from his days as a Royal Air Force mascot, leading Ginger to the idea of creating a flying machine, called the Old Crate, to flee the Tweedys. All the chickens, with help from the rats, secretly assemble the required parts for the plane from their coops while racing against Mr. Tweedy's repairs. While travelling the countryside, Rocky sees a billboard for Mrs. Tweedy's Chicken Pies and is inspired to go back to help.
With the machine now fixed, Mrs. Tweedy insists that Mr. Tweedy gather all the chickens, but the chickens are ready to escape. They knock Mr. Tweedy out and tie him up long enough to complete assembly of their plane. Just before they take off, Rocky returns and joins them. As they are taking off, Mrs. Tweedy chases them down and catches onto a Christmas light strand snagged in the wheels. Mrs. Tweedy climbs the strand, intent on chopping Ginger's head off, while Ginger races to sever the strand. Ginger manages to trick Mrs. Tweedy into cutting the strand with her axe and sends her straight into the vent of the pie machine, causing it to explode. The force of the escaping gravy demolishes the barn they had constructed it in.
Later, the chickens have found a quiet island where they can enjoy their freedom and raise their chicks, while Ginger and Rocky have developed a romantic relationship. Nick and Fetcher decide to start their own chicken farm for eggs but disagree on whether to have the chicken or the egg first.

Question: What demolished the barn?
Answer: The force of the escaping gravy