Moe's facial expression changes when he finds out about the soup the Stooges are eating.
When the Stooges are running after seeing Bob O. Link's body, Larry is in his socks. When the Stooges are banging on the door to get out, Larry has his shoes on. When they go back to the room, he's in his stocking feet again.
When the Stooges are coming down the stairs and crash into the maid, it is obvious that it is not Curly, but his stunt double.
When Moe strikes a match on Curly's neck, his reaction is delayed.
Larry accidentally hits Moe in the eye when he and Curly are saluting the detective and Moe's eye is visibly swollen for a few seconds.
When Curly is supposed to accidentally smash the detective with the chair, the actor clearly is tilting his head to anticipate the hit.
When the Stooges are singing "Let's go get the moolah." Curly goofs up the first time and says "dough" instead.
When Curly says the line, "Stand aside, I'll break the door down!", his mouth does not match the line.
When the parrot in the bed sheet is seen flying around the room, you can see the wire attached to it.