At 38minutes into the film Gloria Dickson's "Peggy" calls John Garfield's character "Johnnie" when he in fact is still under the guise & alias persona of "Jack Dorney"! She could not know that since he has not told anyone at that point of the film.
When "Jack Dorney" and some of the kids were trapped in the water tank, they swam to the bottom of the tank to lift a drain cap to let out the water so they wouldn't drown. Of course, the pressure of 10 feet of water in the tank would have exerted 500-600 pounds per square foot on that drain cap, making it much more difficult if not impossible for them to lift it.
In the diner scene when Johnny drops the $50 note, one of the other diners (Bill) claims the money saying "... That's not your money - that's my money". An actor in the background can be seen mouthing Bill's lines at the same time as Bill utters them.