Continuity mistake: The morning Josh becomes big, one of his sneakers in the bedroom swaps from being underneath the bed by the coat sleeve, to half a meter away in a different position.
Continuity mistake: When Tom Hanks and his boss are playing the oversized piano, a young girl in the background is seen to sit on her dad's lap twice. Also, the boy in the sweater disappears, then reappears in time to applaud at the end of the song.
Continuity mistake: When Josh and Billy arrive at the hotel, the concierge takes his hand with a cigarette to his mouth, but from opposite angle his hand is down counting the money.
Other mistake: Josh's birthday, according to the milk carton, is in the winter. But, some time after he celebrates his birthday at the Italian restaurant, he returns to his childhood neighborhood and it's fall (colored leaves, etc.). It can't be the following year because he's only gone for a total of a few weeks.
Continuity mistake: When Elizabeth Perkins sleeps over at Josh's loft, the pillows behind her head are flat and in the middle at the head of the bed. When they cut back from Josh, they are pushed up in the corner of the bed.
Other mistake: When Josh and Billy are over the balcony dropping the water balloon on the mover on the street, the balloon is shown dropping from an overhead angle off course from hitting the man below, yet we hear him scream being hit, when it easily would have missed him where Josh dropped it.
Revealing mistake: After young Josh is granted the Zoltar wish he drops the cable. In the following shot of him walking away not only it is not next to the machine, but it runs along the concrete, revealing it is plugged somewhere offscreen.
Continuity mistake: When Josh and Susan talk about the electronic magazine at Susan's place, the slice of pizza on the plate moves between shots.
Continuity mistake: When Josh and Susan arrive at Josh's apartment, the distance between Susan and the dinosaur changes twice between shots.
Continuity mistake: Josh stumbles into McMillan, scattering papers everywhere. Susan picks up hers and presses them against her chest. In a close-up they're tidy, yet a shot later they're all messed up.
Audio problem: When Josh is about to be interviewed, a woman says "Personnel director would like to see you now" but she's not mouthing the lines.
Continuity mistake: While Billy and Josh read the newspaper ads, note Billy's ice cream: the spoon stands-out longer or shorter and the pattern of the chocolate differs between shots.
Continuity mistake: In the equipment room, after adult Josh sings to Billy, his hair swaps from messy to brushed right before he says "Josh you look terrible."
Continuity mistake: When Billy enters the equipment room and confronts adult Josh, note the top ball's yellow sticker: it's either facing his face or away, depending on the angle.
Continuity mistake: Before adult Josh leaves home, he grabs Zoltar's card by twisting his hand around. In the close-up, the hand's position is different.
Factual error: The closing credits give thanks to "FAO Schwartz", misspelling the name of the famous toy store with an extra "T".
Answer: When Josh started at the toy company, he torpedoed Paul's skyscraper transformer by saying 'I don't get it.' Paul is returning the favor.
Brian Katcher