Continuity mistake: The angle from which Scorpio shoots the girl in the swimming pool does not match the way she is hit in the shoulder. (00:01:40)
Continuity mistake: When Scorpio shoots the girl in the pool a red towel is spread over the backrest of the right deckchair. When the police officers are dealing with the girl's body the towel is crumpled in the seat of the chair, but when Harry looks at the pool from the other building the towel is again spread out as before. (00:02:00 - 00:04:30)
Continuity mistake: When Scorpio shoots the girl in the pool she is swimming in the middle, but in all later shots the water is only bloody at the steps where she was pulled out. (00:02:05)
Revealing mistake: In the sidewalk scene, after one of the robbers leaves the bank and dives into the car, and it drives towards Harry, you can see a wire rope that appears to have been used to either stop the car from going too far or has been used to help roll the car. (00:02:07)
Visible crew/equipment: When the car with the bank robbers drives off Harry shoots the driver. The car crashes in a flower stand and knocks over a hydrant. When the camera angle changes to a view from the back you see a cable coming out of the trunk. (00:11:55)
Continuity mistake: In the early scene when Harry walks across the street to confront the wounded robber on the street ("Did he fire six shots or only five?"), the shotgun used by the robber is lying several feet from the robber's hand, but when he reaches the robber, the camera shot shows the shotgun just a few inches from the robber's left hand. (00:13:00)
Factual error: When Harry is confronting the bank robber and the robber says he has to know if Harry had any shots left, Harry cocks the hammer which rotates the cylinder. If you watch closely when he pulls the trigger the cylinder rotates again. This can happen only when the trigger is pulled in double action mode (hammer down). (00:14:00)
Other mistake: According to the big photograph in their respective offices Bressler and the DA share the same pair of little daughters. (00:17:05 - 01:10:10)
Continuity mistake: When the jumper jumps over to the cabin in which Harry was lifted up, Harry knocks him out, securing the man by holding his arm over the top railing. When they arrive on the ground he is holding the man's arm over the lower railing, which raises the question how and especially why he moved the unconscious man down while he was hanging outside the cabin. (00:31:10)
Continuity mistake: When Harry asks Bressler for some scotch tape to fix the knife to his leg the tape holder turns around before Bressler picks it up. (00:44:50)
Continuity mistake: When Harry is standing in front of the cross the light comes from behind. When the camera angle changes as Scorpio walks up to him the light comes from the side. (00:56:15)
Continuity mistake: During the scene on the football pitch where Callahan is torturing Scorpio to force him to say where the kidnapped girl is, there are several shots as if from Callahan's viewpoint. As the camera switches between the two characters, the white painted lines on the pitch mysteriously move or even vanish underneath Scorpio. (01:06:50)
Revealing mistake: Near the end the psycho killer pays a black man to beat him up so that he can then blame the injuries on Dirty Harry. Watch the killer's hairdo as he gets punched and beaten: a couple of rear-view scenes show an obviously fake wig, intended to look like the killer's own bad-hair-day style. (01:16:05)
Character mistake: When Scorpio hijacks the school bus near the end, he says something to the effect that they are going to take Sir Francis Drake Boulevard to the Santa Rosa Airport. Unfortunately, Sir Francis Drake Boulevard doesn't go anywhere near Santa Rosa, it heads west through Marin County and ends up near Pt. Reyes. They should have stayed on the highway and kept going north to get to Santa Rosa. (01:27:25)
Continuity mistake: When Scorpio leaves the hospital after treatment of his face injuries he has a band aid over his nose and a rectangular gash on the forehead. When he kidnaps the bus the tape is higher up his nose, and after he hits the little boy it is shorter. The gash on the forehead turns triangular at the end before they crash into the gravel pit area. (01:30:00)
Continuity mistake: In the scene where Scorpio takes the fishing boy hostage the shrubs behind Scorpio keep changing. Actually, there shouldn't be any as he is standing right at the edge of the lake. (01:34:45)
Revealing mistake: When Harry kills Scorpio with the last bullet the deadly wounded Scorpio looks back over his shoulder while he is flying into the lake to prepare for the dive. (01:36:15)
Continuity mistake: When Scorpio falls into the lake the ripples he creates disappear within seconds, but when the camera angle changes the ripples are back and there a lots of leaves floating on the water which weren't there before. (01:36:20)
Other mistake: When Callahan is going to deliver the yellow bag containing the money to Scorpio, he tapes a knife to his leg with sellotape. However, later when he uses the knife to stab Scorpio in the leg, there is no sellotape on his leg.
Character mistake: The bus driver identifies herself as Marcella Platt, but after they get off the phone, the cop who checks her out calls her Priscilla Platt.
Answer: He certainly knew at the start, which is why he felt confident in pointing the gun at the (disarmed) robber and pulling the trigger. Harry knew he was bluffing, but passed it off so well the robber wasn't sure. At the end of the film, again, he knew he had one bullet left and wanted to bait Scorpio into attacking him, giving him an excuse to fire.