The cue ball changes position on the table between the few seconds the other balls have been pocketed and after PIP appears.
When Rocky kicks the women out and slams the door, the entire wall shakes. Then, when he is trying to open the door, the wall and door frame move along with the door.
The filament used to lift the cover of the record player is visible although it's quite thin.
When Rocky shoots the lamp, the light goes out and the lamp smashes a split second after he fires the gun (even more clearly in slow motion), but at that very close range, those effects should be perceived as instantaneous.
The billiard scene is obviously a product of stop-motion animation. Some of the balls disappear near the holes rather than falling into them.
Henry is wearing his porkpie hat backwards. The bow is always worn to the left.