When Perry meets Lt. Tragg immediately after Barker's murder, Tragg shows Mason the fatal bullet and claims the gun from which it was fired is registered to Sylvia Oxman. But there is no way to identify a specific firearm from its bullet alone.
In the last scene, Paul states that there are 36 numbers on Della's roulette wheel. That is incorrect. There are either 37 (Europe) or 38 (American) numbers, which is where the house gets its advantage, either 2.7% or 5.26%.
After Perry arrives at Frank Oxmans apartment, as he enters and Oxman closes the door. A bust can be seen in the corner behind the door, it's facing the wall.
If you watch a better print of Perry entering Frank Oxman's apartment you can see that the bust always faces the center of the room. Because the bust is black the face may be difficult to see.
If you watch a better print of Perry entering Frank Oxman's apartment you can see that the bust always faces the center of the room. Because the bust is black the face may be difficult to see.
When Perry goes to push the door buzzer of Frank Oxman's apartment, the sound of the buzzer is heard before he presses it.
Perry knew before going to the casino that Barker had started a bidding war over Sylvia Oxman's IOU's. Barker would already have contacted Frank Oxman to take his bid, so Perry should not have tried a bluff in which Paul Drake impersonates Frank (or, at least, should have expressed his doubts over whether it would work).
Perry asks Duncan how his casino receives its cut from customers. Perry shouldn't have to ask, because he played poker at the casino the preceding evening.