Revealing mistake: When Johnny, Marco, and Chet are all on top of Al, the big guy who has a chemically induced psychosis, while Roy injects Al with diazepam we can see the outline of the knee pad that Marco is wearing under his pants. As an aside it's funny to watch Chet's face hamming it up during this scene.
Revealing mistake: While the squad and engine are en route to "possible fire", one of the camera angles is from the POV behind Roy and John, where the back of squad is located. That’s fine, but the problem is that there's bright sunlight on their backs as they’re driving, when it should not be there. Artistic license is acceptable, but with so much sunlight where it should not be it reveals that Squad 51 is not in its normal state.
Revealing mistake: When Johnny, Roy, Vince, and the wounded officer are hiding between the bakery truck and car, before the multiple bullet holes actually appear on the side of the truck, those areas where the holes will show up have off-color markings, prepared for the stunt.
Revealing mistake: When Roy's in the ambulance with the man who was rescued from under The Boat, he's on the Biophone with Rampart, and just after Roy says, "So we've occluded the arterial flow in the right arm," in the next shot from inside the ambulance, we can see that they pass a couple of parked GlamourTrams. The ambulance drives around Universal's lot while shooting the footage inside the moving ambulance, en route to Rampart.
Revealing mistake: When John is in the moving ambulance with the pregnant gunshot victim, Brackett asks him if he hears fetal heart tones, and when John removes the stethoscope from his ears he leans back and we can see out the window that the ambulance is quite stationery, despite the siren.
Revealing mistake: When Johnny and Roy are at the top of the open drawbridge, Johnny is wearing a watch on his left wrist, but when his stunt double rescues the woman in the car dangling off the edge, he is not wearing a watch. Additionally, the stuntman's pompier belt has a large axe sheath attached to it, but Johnny's life belt does not, and the stuntman's arms are much hairier, as usual.
Revealing mistake: When they wheel the stretcher with the unconscious teenager from the school fire into treatment 3, the stretcher is pushed up against the ER's gurney, and when the teen's right arm gets caught between the stretcher and gurney, the supposedly unconscious teen moves his arm up out of the way. Then he lifts his left hand when the attendant removes the blanket.
Revealing mistake: When Squad 51 gets back to the station, while Johnny's trying to convince Roy to coach their singing, the usually highly reflective chrome surface of the spotlights have been sprayed with a dulling spray, to temporarily dull the finish for this shot.
Revealing mistake: When Squad 51 leaves Rampart, in the first interior shot facing Roy as John says, "Yeah, I'll tell ya, when it hits ya... Boy when I met Valerie it hit me," through the back window we can see movement at the back of the squad. But in the shot facing Roy when John says, "So that's that... That's exactly how it is," through that back window we can actually see a crew member's face (sideways), who has a mustache, right behind John's head, as he's riding on the back of the moving squad. It's so funny, have a look.
Revealing mistake: When Station 51 is dispatched to the bomb threat, just as they roll up on scene, in this specific POV the corner edges of the screen are blacked out due to the lens that was used, but when it cuts to other angles it's gone, then it reappears with that POV. We see it three times.
Revealing mistake: After Station 51 is dispatched to the 'plane in trouble' it becomes a plane crash rescue and recovery, and when they pull out the pilot's body, who they said died on impact, his right hand moves to clasp his left wrist, and he also bends and moves his leg.
Revealing mistake: At the apartment complex fire, after Johnny is knocked unconscious by the explosion, when the Pasadena fireman finds him and has to lift him up, it's funny how even though Johnny's unconscious we can see that he actually helps to stand himself up, so the fireman can lift him up and carry him out.
Revealing mistake: After Station 51 is dispatched to the 'plane crash into a structure', when Engine 51 pulls over to lay the dual lines at the hydrant, we can see up the block on the left, the back side of the apartment complex where they are headed, and most of the back windows are boarded up. The following scene takes place at the front doors of those apartments, where people supposedly live. The show used some real locations (not just Universal's sets) where there had been real fires, to film carefully controlled fire scenes.
Revealing mistake: During the fire at the apartment complex, there are strips of black material nailed to the tops of windows where the FX fire shoots out from below, and the doorway Roy passes when he's pulling on the hose has a fake ceiling and wall nailed directly into the door jamb, to control the strip of FX fire at the side.
Revealing mistake: At the apartment complex fire, just as Chet climbs the ladder and Marco holds the top of the ladder on the second floor balcony, we see the plumes of FX smoke spurting from the side inside the doorway behind them, and even see something quickly fanning the smoke.
Revealing mistake: At the start of the episode, we see Squad 51 speeding toward their destination, and when the camera cuts to the woman in front of the market, she's waving her arms to the squad somewhere in the distance. But notice that while Rosa is looking to her left and waving, we can see Squad 51's reflection in the window (with the liquor bottles), as they are parked right there, just off-screen waiting for their cue to "speedily" pull up.
Revealing mistake: When the Bengal tiger is on the roof, just after the officer warns, "If that cat tries to leave this roof, he's dead before he hits the street," there is a closeup of the tiger and the empty landing below the billboard. A few shots later, after Les steps on the glass, there are pieces of meat scattered on the landing below the billboard, so the trained tiger will jump onto it.