An Ounce of Prevention - S6-E13
Continuity mistake: When Roy and Johnny are rehearsing in front of Captain Stanley and the other guys, after Johnny uses the bug spray on the flame, in the wide shots Roy's hands are in his pockets and the hairspray can is on the table, but in the closeups Roy's still holding the hairspray can.
Other mistake: When Station 51 is dispatched to the "freeway accident," as the engine and squad roll out of the apparatus bay, we can see the real 127's vehicle still parked in the bay, near the rear door.
Visible crew/equipment: When Station 51 is on scene at the freeway accident, after the two girls are rescued from the wreck, when the explosion occurs Roy and John dive to the ground, and as the camera zooms out we can see the top of the location's array lighting unit, just past the engine's hose bed at the bottom left corner.
Visible crew/equipment: During the rescue at the jail, while Roy is hanging on the line, the outline of the mic transmitter is visible on his shirt at his left side.
Revealing mistake: During the rescue at the jail, while Roy tries to get a safety belt around the prisoner's waist, the man freaks out, then grabs Roy and they both swing out on Roy's safety line. When the camera pans a bit too far to the left, we can see the edge of the fake "sky" screen on the left, behind the building's replica set used for closeups.
Fair Fight - S6-E5
Visible crew/equipment: When Johnny and Roy get back to the station and walk into the day room, right after Marco says, "Well, either he's sick, or he's the laziest dog ever lived," we can see the shadow of the boom mic moving back and forth across the top of the wall, on the right.
Visible crew/equipment: After Station 51 is dispatched to the fire at a singles club, when Engine 51 pulls into the parking lot it and then turns around, the reflections of multiple array lighting can be seen on the engine's surface and Mike's window when he opens the door.
Other mistake: When the self defense instructor tries to use Mrs. Pestone to demonstrate the flip, he puts his arm around her and covers her mouth, then it cuts to a shot of Squad 51 rushing down a street. This particular shot is from 5x8, "The Lighter-Than-Air Man," when Roy drives past the school kids and crossing guard.
Other mistake: During the singles club fire, after Johnny and Roy check the men's room upstairs, there's a shot of firemen in full turnout gear with hoses, and this footage is from the first season's pilot episode, "The Wedsworth-Townsend Act."
Other mistake: During the actual cliff rescue of the hang gliding accident victims, Roy and John are wearing hiking-type shoes with ridges on the soles, not their uniform shoes.
Loose Ends - S6-E12
Visible crew/equipment: During the fire at the train yard, when they carry out the second toxic fume inhalation victim from the boxcar, just before they pass the camera, the shadow of the camera tracking backwards is visible on the boxcar, to the left.
Paper Work - S6-E11
Other mistake: When Marco is taking inventory of what's in the refrigerator, the containers on the door have their brand names covered.
Visible crew/equipment: When Station 51 is being dispatched to 'auto accident with injuries' there's a closeup of Sam Lanier, the dispatcher, and in the next overhead shot of the apparatus bay, we can see the reflection/shadow of equipment moving on Engine 51's windshield, at the bottom left corner.
Continuity mistake: While Roy and John are with the man whose back went out, when Thadeus runs off with the BP cuff and Roy chases him, Roy has the stethoscope around his neck with the chest piece hanging down, but once Roy falls into the pool the chest piece is suddenly tucked down into the front of Roy's shirt.
Captain Hook - S6-E8
Visible crew/equipment: When Roy, John, and Chet are standing near the stove talking about Hookrader's party, just as John tells Chet, "And you! You with that speech!" they walk towards the table, and the shadow of the overhead boom mic swoops across the cabinets on the right.
Visible crew/equipment: When the police officer who was struck by lightning is wheeled into the ER, just as Dixie, Brackett, and Early walk up the hallway, the two tape marks are visible on the floor right outside the doorway of treatment 2, where Dixie is about to stand. Additionally, we can see the outline of the transmitter wire on the back of Dixie's uniform.
Revealing mistake: When Dixie's in the basement asking Gary why the lab is still backed up, the next shot shows the plumber working in the cabinet under the sink, but when it cuts to the next shot the plumber is gone, his tool box is closed, things are different/missing from the counters, and the tables and stools have been turned over with a mess all around, before the explosion even occurs.
Other mistake: When all the guys are sitting around the table discussing the paramedic problem, while Chet is looking in the fridge for the ketchup, we can see the milk containers on the door have their brand names covered.
Other mistake: While Roy's in the ambulance with the woman who fainted, when she holds out the bag of potato chips, we can see the large brand name on the front of the bag is covered with red tape in two places. Though they neglected to cover the small 'Lays' brand name on the side of the bag.
Other mistake: At the start, while Johnny is cleaning the oven, we can see that the oven cleaner spray can has tape covering its brand name, and anything else on the can that gives away the name of the brand.
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.