Weird Science Movie Pictures Chet
Continuity mistake: During the storm of Lisa's creation, when Wyatt shouts to hang up the phone, Gary leans over Wyatt's arm and places the handset back onto the phone base. However, after Gary shouts, "What's going on?" the handset is still on the modem.
Super Grover 
Revealing mistake: When Gary and Wyatt come home and see Chet turned into a pile of poo, Chet shoots his tongue from his mouth and catches a fly. Look closely, the tongue flies completely out of his mouth and is attached to a metal spring. (01:24:55)
Continuity mistake: When Chet gets home the morning after the big party, he does an about face at the bedroom door and starts to kick it open on one side. On the inside of the bedroom door, it shows Chet actually kicked the door in on the opposite side. (00:25:05)
Lynette Carrington
Other mistake: In the mall scene, when Gary and Wyatt sit down on the bench and Max and Ian dump the Icee on them, notice how much slush is actually dumped on them from a 32 oz. cup. (00:32:55)
Continuity mistake: In the scene where Wyatt and Gary are taking Deb and Hilly home in the Ferrari and Porsche, Gary is being pursued by the police. When Gary approaches the railroad tracks, the train is shown coming in the direction of the passenger side door. When they finally cross over the tracks, the shot is flipped, and the train is seen to have crossed the intersection in the direction of the driver's side door. (01:19:25)
Other mistake: Garry and Wyatt are sitting on the side of a 'planter box prop' that was built for the movie, not a bench, when Ian and Max spill the Icee (slush) on them. (00:32:52)
Revealing mistake: Arriving home from his hunting trip, Chet Donelly (Bill Paxton) finds Gary in bed with a girl. Chet whacks them both over the head with his rifle and you can clearly see the barrel bend with each hit. (01:13:54)
Continuity mistake: When Gary grabs the FDX system unit (Memotech), the monitor (with green text) which sits atop the system unit falls backwards, and he then throws the system unit out the window. However, the FDX unit is back on the desk, with the monitor atop it (they are between the display monitor and feed scanner), when the boys are on the floor.
Super Grover
Continuity mistake: Lisa is trying to convince Gary's parents to let him go to the party. There is a glass of beer on the table. The camera switches to a close up and then back to a wide shot and the beer is gone. (00:37:49 - 00:39:10)
Continuity mistake: When the four guys are waiting for the second doll-woman to appear, Gary's hand jumps from sitting on his leg to being up by his chin. (00:55:45)
Continuity mistake: When the ritual candles are first seen, one of them sits in a white corner area of the Life boxtop. In a later shot the candle moves in and sits on (newly appearing) black text. (00:10:35 - 00:11:20)
Continuity mistake: When Lisa's confronting Gary's father, her hands rest on her hips as clenched fists. As Gary sits down after being told to shut up, Lisa's hand is open palmed. (00:39:55)
Continuity mistake: In the scene where Gary has come home drunk, he reaches out to touch Chet's face. In the initial shot of him reaching out, he's using his right hand, then when they show a closeup of the gloved hand on the face, it's the left hand. (00:24:02)
Continuity mistake: As Gary & Wyatt get up to leave the Kandy Bar, some of the guys stand up also to joke around and make bets. In the following shot the men are still in their seats. (00:20:55)
Continuity mistake: There aren't any shoes on the Lisa doll, but the real life Lisa appears wearing high heels. (00:11:20 - 00:12:55)
Continuity mistake: Lisa has just exited the shopping mall. Gary pulls up in the Porsche. When Gary pulls up onto the curb, the cars behind the Porsche include A white coupe, a blue sedan, a silver Chevy Monza and a brown Lincoln Town Car. Gary gets out of the Porsche and says " Lis' we're running late" and the cars have completely changed except the silver Chevy Monza. Lisa turns to get into the Porsche and the cars behind them have completely changed yet again. Now they include a Brown Van and a silver 4 door Plymouth Horizon. Obviously the mall parking lot was not closed during filming, and this 2 minute scene was shot over the course of several hours. (00:35:40)
Continuity mistake: When Lisa shows Wyatt & Gary the grandparents in the pantry, her arms are folded - but as Gary & Wyatt are leaving, Lisa's hand is holding the pantry door open. (00:59:40)
Continuity mistake: In the gym, when Ian and Max walk up behind Gary and Wyatt, there is a closeup of their feet, and we see that the left laces on Gary's high tops are laced all the way up, tied snugly. However, when Ian and Max pull down the boys' shorts, in this close-up Gary's laces are only midway up the high top's eyelets, loose and untied. (00:01:25)
Super Grover
Continuity mistake: After the party, when Chet gets out of the vehicle, he has five shotgun shells in the front of his vest. As he walks up the stairs, he has three shotgun shells in his vest. A few seconds he opens his bedroom door and he has five shotgun shells in his vest again. (01:14:45)
Kaltenmeyer
Continuity mistake: When Chet and Wyatt are in the kitchen getting breakfast, the paper towels in the background are all rolled up. From the point when Chet says, "That's not a joke," a loose paper towel is hanging down from the roll. (00:29:50)
More for Weird Science
Quotes
Wyatt: By the way, why are we wearing bras on our heads?
Gary: It's ceremonial.
[Later, after Wyatt talks to Chet, Wyatt begins to leave the kitchen and Chet sees him wearing women's underwear.]
Chet: Like your panties.
Wyatt: [walking back into kitchen] It's a joke, Chet. Really.
Chet: No. That is not a joke. That is a severe behavioral disorder. Next thing you know you'll be wearing a bra on your head.
More quotes from Weird Science
More trivia for Weird Science
Questions
Question: At the very end when Lisa is a gym instructor, when they pan from her feet up, on VHS and on my DVD the Rocky theme is played. But whenever I see it on cable, the Weird Science theme is played instead. Why is this?
Carl Missouri
Chosen answer: They probably only had permission to use the song at the cinema and take home releases, so when shown on broadcast TV they'd have to use another song.
More questions & answers from Weird Science
Weird Science Movie Pictures Chet
Source: https://www.moviemistakes.com/film1601