Two of my favorite things in this short:
1. The business when the Stooges use the shave-and-a-haircut knock to get into the jail only to get a punch in the face. The swiftness with which the punch follows upon the knock and the fact that we never see the face or body of the owner of the fist (yes, we just saw Eddie Laughton in the doorway a moment before, but we don't see him now) makes it seem as if the punch in the face is a direct mechanical effect of the knock rather than the chosen action of a human being. Of course, Curly thinks he can do it better than Moe: "Let a fellow who knows how to knock, knock, nick, nack, nyuk, nyuk, nyuk, nyuk—" (punch in the face). A similar gag will occur in Three Hams on Rye, when Shemp encounters a door with words on it that he deciphers as "Dangerooz, kippawah!" ("Dangerous—keep away"), opens it, and gets a boxing-glove-clad fist right in the face for no reason that is ever explained.
2. Barbara Slater. Hubba hubba. She looks as if she really likes Curly!