Continuity mistake: When Fred (Ralph Wolf in disguise) says "Hello" to Sam at the end of the short, you can see that there is a card in both the top and bottom holes in the "In" section of the punch clock. But when Sam begins spanking Ralph, the bottom card of the "In" section has moved to the bottom hole of the "Out" section.
Continuity mistake: When the whistle goes for 5 o'clock on the punch clock, you can see that the hour hand is on the "12", but in the next shot it is now on the "1."
