Revealing mistake: Anytime the kids are shown running through the backyard, it sounds very obvious they are running on a wooden set floor instead of real grass-covered ground.
Baby, It's Cold Outside - S1-E18
Revealing mistake: When Wilson and Tim start to talk they sit down on some rocks. If you look at Wilson's foot you can see the sheet of fake snow caught under his foot.
Revealing mistake: Towards the end of episode 2.18, "Bye, Bye Birdie", Tim drops to the ground in the back yard while trying to avoid the helicopter. When Tim gets up, you can see the grass (carpet) move and wrinkle up.
Ye Olde Shoppe Teacher - S4-E10
Revealing mistake: In this episode, every time Wilson places a log on the block before splitting it, you can see a dark line on top of the log, showing where they were pre-cut.
Revealing mistake: When Tim is falling, crawling and rolling on the snow-covered ground in the final scene, none of the snow clings to him or his clothing. He does not even get damp, even when he is lying on his back in the same spot for several seconds.
Revealing mistake: At the beginning during the Binford commercial, Tim falls off the ladder that they just set up and it's possible to see it's connected to the wall (so it will flip, but not fall over).
Revealing mistake: When Tim gives Jill the framed photo of the two of them on their way to the Doobie Brothers concert, you can tell Tim has just been photoshopped into an existing picture of Patricia Richardson, as he is slightly out of focus despite the fact that they are standing next to each other. (00:13:24)
Revealing mistake: At the end of the episode before Tim opens the front door for Julie Zwicky, you can see the actress' silhouette in the window pane for several moments before she rings the doorbell, showing her to be waiting for her cue.
Revealing mistake: At the beginning when Tim goes to throw the debris out of the window of the house they are remodeling, it's obvious that Tim is replaced with a stunt double.
The Karate Kid Returns - S6-E14
Revealing mistake: When the box falls on the kid's head, Randy and Mark run out of the store. When they run out, the mall stores in the background wave or move revealing that it's not an actual mall set but just a backdrop.
Revealing mistake: When the hot rod is back in the garage covered in "snow" - look at the color of the car, along with the door when the door is open. There is plastic on the inside of the door (probably to get all of the snow off so quickly) and the color of the hot rod is a lighter shade of blue then normal.
Maybe, Baby - S3-E1
Revealing mistake: Whenever the door to the garage is opened the garage is not quite what it should be. It looks like there is a wall just inside the door.
Revealing mistake: At the very ending of the episode, when Tim runs through the back wooden fence, just before he hits the fence, you can see the loose board fall from top to the bottom and towards him before he even hits the fence.
Revealing mistake: At the end when Tim and Marty are outside Marty drops the ladder supposedly on Tim's foot, but it never lands close enough to his foot for Tim to get hurt.
Revealing mistake: Just before the dish explodes out of the dishwasher through the wall the cut out that was made to allow that to happen is visible.
Revealing mistake: When Randy is thrown across the yard by Jason and his friend, you can tell that he is actually just launching himself as you can hear him take four running steps after Brad says "Hey Wilson, how's it going?", followed by Randy appearing onscreen and then jumping off the porch. You can also see Randy's lone shadow running towards the spot where he jumps from while he himself is offscreen. Next you can tell he lands on a crash mat because the leaves on the ground drag behind him as he is sliding across the grass. Lastly, after he says "I'm going to get you for this Brad!", you can see him walking towards the gazebo where Jason and his friend are sitting and just before the shot changes Jason extends his left hand for Randy to give him five.
Answer: No the guy sent in a picture of himself because he thought he looked like Al. So they brought him on the show as his brother.
Bowling255 ★