Camera Bug - S4-E10
Other mistake: When Engine 51 and Squad 51 first roll in during the school fire, we see the burning building has a flat roof. After Johnny and Roy have rescued the unconscious boy from the classroom, there is a closeup of two firemen standing on a slanted, tiled roof with a hose, which is from episode 3x2, "The Old Engine", just before 17's Captain Harmell falls through the warehouse roof.
Camera Bug - S4-E10
Visible crew/equipment: After Johnny snaps the picture of Marco on the engine, when he prods Chet to go stand by the map, as the camera moves to the left we can see the reflection of production equipment/crew on the back of the squad, and we can even make out the shape of someone seated on a director's chair.
Camera Bug - S4-E10
Visible crew/equipment: When the stretcher with the unconscious teenager from the school fire is wheeled into the ER, while Roy is using the Ambu bag, just before they reach treatment 3 we can see the top of the set down the hall, near the nurses' station.
Camera Bug - S4-E10
Other mistake: While Roy and John are at 68's, Roy goes to the stove to see what Bob was cooking when he started having pain, and the closeup footage we see of the pot of bubbling chilli is the same as some of the footage of Chet's chilli in 4x1, "The Screenwriter," when 'Miss October' stops by the station.
Camera Bug - S4-E10
Other mistake: At the end of the episode, when Johnny's telling the other guys that his photograph was bought, the box of cereal and carton of milk that are on the table have tape affixed to them, to deliberately cover their brand names.
Camera Bug - S4-E10
Visible crew/equipment: At the accident scene with the truck carrying dynamite, when Roy is leaning over the driver's door, the outline of the mic transmitter is visible on the back, right side of his shirt. Then, when they're carrying the driver to the top, Johnny's becomes visible at his left side.
Camera Bug - S4-E10
Visible crew/equipment: When Johnny is driving Roy nuts by taking closeup pictures of him checking the squad's engine, the outline of the lavalier mic wire is visible on Johnny's back.
Camera Bug - S4-E10
Visible crew/equipment: At the school fire, when Johnny is administering the O2 to the teenager with smoke inhalation, the bulging outlines of the mic transmitter and wire are visible on the back, left side of Johnny's shirt.
Camera Bug - S4-E10
Continuity mistake: When Roy's using the Ambu bag on the unconscious teenager from the school fire, while the stretcher's being wheeled to treatment 3's door, Roy has a stethoscope hanging around his neck, but in the next shot as they enter treatment 3 the stethoscope has vanished.
Camera Bug - S4-E10
Visible crew/equipment: After Johnny tries to take Chet's picture beside the map, when Captain Stanley walks from the office to the back of Squad 51, the reflection of crew/equipment are visible on the back of the squad.
Camera Bug - S4-E10
Continuity mistake: After Roy and Johnny are dispatched to Station 68, Bob is lying on the floor with his shirt buttoned up and Roy has his hand on Bob's chest taking his respiration, but when it cuts to Bob's closeup his shirt is already unbuttoned, with the ECG electrode discs and leads in place on his chest. Additionally, in Bob's closeups the leads go from attached to the discs, to unattached, to attached again.
Camera Bug - S4-E10
Continuity mistake: When Johnny's leaning through the windshield of the truck carrying dynamite, using the jaws to free the driver, Marco's behind Johnny with the hose fogging them down, and Johnny's clothes get soaked, but in the closeup as Johnny pulls the driver from his seat, Johnny's shirt is completely dry.
Camera Bug - S4-E10
Visible crew/equipment: At the start of the episode, when Johnny is taking photos of Roy in the locker room, the actor's tape mark is visible on the floor below the bench, where Johnny stands when he shows Roy the article in the newspaper supplement.
Visible crew/equipment: When all the guys are talking to Mr. Gibson, who is stuck in the trench he fell into, the outlines of the lav mic transmitters are visible on the backs of Roy's and Johnny's shirts.
Continuity mistake: When Dr. Morton leaves the room of the patient who attempted suicide to get Jack, he takes the pill bottle from Dr. Early, carries the medical chart holder, and is wearing a stethoscope around his neck, but in the hallway when he gets Jack the pill bottle and chart holder are gone, and the stethoscope is in his pocket. Then, when they walk back into the room, Morton's holding the bottle and chart holder, and the stethoscope is back around his neck.
Visible crew/equipment: When Station 51 is dispatched to a man over the cliff, while en route there's a shot from the top of Engine 51, with the dome light in front of the camera, and the reflection of the covered camera, which is mounted on the engine's roof, is visible in the dome light's chrome surface.
Continuity mistake: While Johnny tries to reach the man who fell over the cliff, when the bicycle falls to the bottom of the canyon both tires break free from the frame, but when the officer retrieves the bicycle, only one of the tires is off, the other is undamaged and on the frame.
Continuity mistake: While Johnny is trying to reach the man who fell over the cliff, the bicycle falls all the way to the bottom of the canyon, and then there's a shot of the man and we can see that the bicycle is still above him at the side of the cliff, just before Chet says over the HT, "Lower him, Cap, the victim's broken loose."
Continuity mistake: After Squad 51 gets back to the station, Roy and Johnny remain in the squad discussing Roy being the coach, and when the dispatcher drops the tones, we see a closeup of five pair of legs rushing out of the kitchen, even though we should only be seeing four pair of legs, since Roy and Johnny are already in the squad.
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.
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.