The Chain Gang
Mickey Mouse and several other characters are on a prison chain gang, guarded by Pegleg Pete. They break rocks for a while, then Mickey breaks out a harmonica and everyone starts making music and/or dancing. Soon there’s a jail-break, and Mickey’s on the run, tracked by bloodhounds (including his future pet, Pluto, in his first appearance).
Historically important as the first appearance of the dog who would become Pluto — here he is one of two bloodhounds chasing Mickey, with no name and no personality. The character was refined over the next year until he became the studio's most valuable non-speaking performer, which makes this the beginning of a long story.
A prison-break short, with guards, bloodhounds and rifles played for comedy.