Continuity mistake: In the exterior shot of Sal entering the bank, there is a car parked by the door. In the interior shot, the car is not visible behind Sal. This mistake is reversed half a minute later when Sonny enters the bank. There is no car in the exterior shot, but it can be seen in the interior one. (00:04:00)
Continuity mistake: At the very beginning of the movie, Sonny walks towards the bank with the box under his arm. The ribbon is on top facing upwards but in the next shot, when Sonny enters the bank, the box and the ribbon are now on the side. (00:04:32)
Continuity mistake: When Sonny takes his gun out of the long white box, he throws the box cleanly away to his right. There is then a wider angle shot of the bank, and the box is now tangled in the strap of the gun on his left. (00:07:00)
Continuity mistake: When Sonny tells the guard to close the blinds all the other bank employees are lined up against the back wall. A little later, after Sonny has spray painted the CCTV cameras the employees are wandering around in front of the safe and only then does he usher them back against the wall. (00:08:55)
Continuity mistake: Just after Sonny says, of Sal, that "that man bites" a potted plant seems to disappear then reappear from the counter. Sonny and the head cashier are moving down the counter getting the cash from each position as they go and, if you look at the signs on the counter, you can see that some shots are shown out of order; there are some shots of "Maria"'s position (no plant) interleaved with the previous position (with a plant). But the end effect is the same - appearing and disappearing plant. (00:12:20)
Continuity mistake: When the head cashier voluntarily goes back into the bank with Sonny you can see, reflected in the door of the bank, the FBI man standing next to the door of his car. In the next shot he is standing by the red car that is parked behind his. (00:37:05)
Continuity mistake: In the scene in which they discuss Sylvia smoking, the paper on the table is different between shots. In the shots of Sylvia there is some paper near the can on the left. In the shots of Sal, the paper is not there. (01:03:00)
Continuity mistake: When Moretti is talking to Leon in the barbers' shop, Leon's hands change position between shots. For example, when Moretti asks if Leon reported Sonny's abuse to the police, Leon is holding his gown shut with 2 hands, but in the next shot only one. (01:06:45)
Answer: He didn't. He just assumed the cops would try something like that, substituting a cop for the real driver. What he didn't anticpate is that they had substituted cops for everyone around the bus when it arrived, and when he replaced the black driver he would have to (unknowingly) pick a cop, regardless. Incidentally, this part of the story is completely factual, it actually happened that way.