Revealing mistake: When the critical boy who ingested the ant poison is being wheeled into the ER's treatment 3, we can see Johnny laughing, and obviously since absolutely nothing about the situation is funny, we know it's Randolph Mantooth just cutting up during the take.
Revealing mistake: When Cindy and her mother come to see the station, Cindy goes to the closet with the gear, and as she opens the door Cindy starts laughing before Johnny even gets hit by the phantom, and then she glances toward the camera grinning because of the prank.
Revealing mistake: While John's in the ambulance with the boy who ingested the poison, after John inserts the esophageal airway and uses the ambu-bag, just as John says, "Real good," if we look out the window behind the attendant, we can see Universal's GlamourTrams (a set of three trams) driving by in the distance. The footage inside the ambulance was shot while the ambulance drove around Universal's lots.
Revealing mistake: When Station 51 is dispatched to the chimney explosion, en route there is a moving bird's-eye view as the filming chopper follows 51's vehicles making a right turn. On the ground below, there are two people standing beside a blue station wagon, and one points up to the chopper flying overhead.
How Green Was My Thumb? - S3-E17
Revealing mistake: When Roy brings the man with a laryngeal obstruction into the ER and is taken quickly to treatment 1, his head is tilted back and Early places a laryngoscope into the patient's mouth and says that he sees the obstruction. The problem is that we can see that the laryngoscope is actually at the side of the patient's face. Then, when Early uses the forceps to remove the obstruction, once again we can see that it does not go into the patient's mouth.
How Green Was My Thumb? - S3-E17
Revealing mistake: When Roy brings in the man with the laryngeal obstruction (partial dental plate), Morton and Early meet them at receiving, then as they rush the stretcher into treatment 1, it's amusing to note that the treatment room across the hall (treatment 2) has room number 412 on it, and even better, treatment 1 itself has number 411 on its door. Obviously the set was prepped for the following shots, when Johnny follows the nurse onto the 4th floor.
How Green Was My Thumb? - S3-E17
Revealing mistake: When Roy and Johnny are at the nurses' station with Dix, Roy decides to deliver the plant that was left for Mrs. Johnson so he and Johnny get into the elevator, and when Roy says, "Six," the floor indicator light on the control panel turns itself on before Johnny even presses the 6th floor button. That light would not turn on if someone up on the 6th floor pressed for the elevator.
How Green Was My Thumb? - S3-E17
Revealing mistake: After Johnny jumps into the wine vat, when he and Roy pull the drowning man out of the vat we can see the rubber/latex suit the man is wearing under his clothes, when his shirt is lifted up.
Revealing mistake: When Johnny and Roy are in the squad heading to Rampart after freeing the girl's toe from the bathtub, they get dispatched to 'possible electrocution' and we can see the white tape with "Kevin" inside Roy's helmet. (00:37:30)
Propinquity - S3-E20
Revealing mistake: When Johnny and Roy are figuring out how to free the woman trapped in her wrecked car, the flames spread and Johnny's pant leg catches fire, but as he's trying to smother that flame, the strip of fire stunt gel that was smeared on his pant leg is visible.
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.
Daisy's Pick Blind Date - S4-E7
Revealing mistake: When John and Roy bring the hypothermic patient into treatment 3, Morton uses the laryngoscope, but the problem here is that when it's placed we can see that the laryngoscope is actually at the side of the patient's face.
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.
Camera Bug - S4-E10
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 see movement at the back of the squad. Then in the shot facing Roy as John says, "So that's that... That's exactly how it is," through the back window we see a crew member's face (sideways), he has a mustache (John does not have a mustache), right behind John's head, as he's riding atop the back of the moving squad. (00:31:00)
Answer: I believe you are speaking of the old man, Mr. Wilson. He's played by J. Pat O'Malley.
Bishop73
Correct, it was J. Pat O'Malley...he also played the grandfather with his grandson when their rocket exploded, and also played "Old Bill" in the episode with Ann Prentiss, where Gage saves the little girl from the burning tree house, and her mother falls in love with him.