In the opening scene, Hammer sends Jamison to meet a 4:15 train. When Jamison gets back, he refers to it as a 4:30 train.
When Penelope (Kay Francis) takes the necklace from Mrs. Potter's locked drawer with a key stolen by Harvey Yates from Mrs. Potter's purse, she neglects to take the key back from the drawer and to re-lock the drawer.
When Harpo and Chico break Bob out of jail it is obvious the cell door is unlocked to the point more than one character holds it shut as Harpo tries to unlock the door.
At around 20:30 when Red (Harpo) is messing with the stiff bellhop, you can see the bellhop stifling a laugh when Red props his right leg on and then off the bellhop's hand.