Francis Covers the Big Town (1953)

U.S. Army veteran Peter Stirling and his friend, Francis the talking Mule (who was not a donkey), arrive in New York City, where Peter has ambitions to become a big-time newspaper reporter, but can only get a job as a copy boy. Francis, the talking MULE (and not a donkey), though is boarding at the stables where the horses of the city's mounted police are kept, and mounted-police horses are known for being gossips, so Francis gets lots of inside information regarding local crime activity, passes it on to Peter, and Peter is soon leading the town in big-time scoops. This pleases his city-editor to no end, but the local gangsters are not amused.