Aunt Bee's Big Moment - S8-E23
Visible crew/equipment: After Aunt Bee's solo flight, just as the flight instructor walks over and gives Bee the papers as proof that she soloed, the large T-mark (rubber/plastic) is visible on the ground between Bee and the instructor.
Aunt Bee's Big Moment - S8-E23
Visible crew/equipment: After Aunt Bee tells Opie that she will solo the next day, when she sits in the chair to practice her flight maneuvers, the actor's tape mark is visible on the floor beside her feet.
Barney Hosts a Summit Meeting - S8-E21
Visible crew/equipment: When Andy and Barney start to get into their car, the boom mic is reflected in the front window. (00:10:10)
Opie's Group - S8-E9
Visible crew/equipment: After Aunt Bee asks Clara to speak to Opie, in the interior shot just as Clara walks into the house we can see the two tape marks on the floor, where Clara and Opie will stand.
Opie's Group - S8-E9
Visible crew/equipment: After Opie leaves Emmett's shop it cuts to the Taylor dining room as Opie is walking away from the server with salt/pepper shakers, and when he sits down we can see the actor's tape mark on the floor by the server. (00:06:25)
Visible crew/equipment: At the start, while Aunt Bee is ironing the bowling shirt, a chalk T-mark is visible on the floor under Opie's chair.
Andy's Trip to Raleigh - S8-E4
Visible crew/equipment: When Andy gets back from Raleigh and shuts the car door, just as the camera moves in closer we can see the reflections of two crew members (the one wearing a yellowish shirt looks as if he's pushing the camera dolly), on the window behind Andy.
Emmett's Brother-in-Law - S8-E18
Visible crew/equipment: When Ben accompanies Emmett on his first call to Andy, just as they both enter the courthouse, we can see a crew member's hand outside reach out to catch the door as it closes. (00:12:40)
Opie's Group - S8-E9
Visible crew/equipment: While Opie and his band are playing at the party there are shots of the kids dancing, and in the shot of a girl with blonde hair wearing a blue dress, the camera angle is low and we can see the top of the set. (00:10:25)
Visible crew/equipment: After the shot of Milly holding hands with Howard (holding a picnic basket), when it cuts to Goober sitting in front of the courthouse the camera angle is low, so the wood framework and lighting equipment at the top of the courthouse set is visible, just as Andy walks over to Goober. (00:05:30)
Visible crew/equipment: After Andy hatches the plan to have Aunt Bee and her friends pick up their photos at the same time, in the following shot just as Andy walks into the shop, the shadow of the boom mic is moving beside the doorway, at the top left side of the screen.
Visible crew/equipment: After Aunt Bee's flight lands, when it cuts to the hotel lobby there's rug on the floor extending from the front desk to the stairs, but in the next shot as Aunt Bee and her friends walk into the lobby that rug is gone (this doesn't refer to the small rug behind them). Also note the tape mark on the floor where the bellhop stops the luggage trolley.
Visible crew/equipment: When everyone is at the airport before the flight some chalk T-marks are visible on the floor, such as the one between Andy and Helen when Andy takes the picture of Aunt Bee and her friends. (00:08:45)
Opie Steps Up in Class - S8-E5
Visible crew/equipment: When Andy walks into the living room at the Hollander's house, the white tape mark is visible on the floor between Andy's and George's feet.
Opie Steps Up in Class - S8-E5
Visible crew/equipment: When Aunt Bee picks Opie up at Billy's house, while Opie tells her all about lunch we can see the reflection of the camera and crew member, on the car's vent window.
Opie Steps Up in Class - S8-E5
Visible crew/equipment: When Aunt Bee drops Opie off at Billy Hollander's house, just as Opie opens the car door the reflections of a crew member and filming equipment are visible on the door's surface.
Visible crew/equipment: After Andy gets the phone call about Sam's victory, when Sam is pushed to give a speech, a few white tape marks are visible on the floor near the fireplace.
Visible crew/equipment: After Emmett talks to to the diner owner about having the bus stop moved to double his diner business, when Emmett walks down the block, the reflection of the moving camera dolly is visible in the store window.
Visible crew/equipment: When Andy, Howard, and Goober walk into Emmett's shop to tell him that Sam's running for head of City Council, the shadow of the boom mic is moving on the wall behind them, at the top of the screen.
The Wedding - S8-E26
Visible crew/equipment: The night of Howard's party, when the doorbell rings and Howard opens the door for Goober, we can see a crew member's head moving in and out of the shot at the right side of the screen.
Answer: Those "boxes" are valences that used to be very common, before air conditioning. They allow for windows to be open during rain storms. They permit air circulation, without letting the rain in.