When Al goes to see Ruby at the reform school, they initially shake hands and let go. But in the next shot, after the matron leaves, they are still shown shaking hands and letting go again.
When Al and Ruby go to the Elite nightclub, as they are talking about her "lost" purse, the position of the ashtray on the table in the foreground keeps changing between shots.
When Eddie slams the door after tossing Aubrey Mitchell out of the apartment, the wall shakes.
When Eddie bumps into Al and Ruby at the nightclub, he doesn't know her first name; but when he was hiding out in her apartment, he was looking at all the autographed pictures on her wall, each one inscribed "To Ruby."
Everyone pronounces Cincinnati as "Cincinnata." Even as a dialect choice it makes no sense, as none of the characters seem to originate from the same place.