Continuity mistake: In Sid's room, there's a lightbulb hanging over the table (which he turns on when he switches the doll's and pterodactyl's heads), and its electrical cord that hangs beside the lava lamp (filled with toy heads) vanishes and reappears a few times during the scenes there.
Continuity mistake: After Woody tosses the string lights to Andy's toys at the window Mr. Potato Head hangs onto the end of it, but in the shot from behind Andy's toys when Woody's shaking Buzz's arm and imitating his voice, we see the outside of Sid's window and the string lights have vanished, then they reappear.
Revealing mistake: When Woody grabs hold of Buzz and uses his "karate chop action" while they walk backwards to the open door, as Woody says, "Sorry guys, dinner's canceled," in the wideshot of all of Sid's toys pay attention to the chair and table at the right side of the screen. What we're supposed to be seeing is the swivel chair with four legs/wheels (and the red toolbox resting on the seat) that's positioned in front of the table's angled wood two-by-four legs. But we don't see that. What we do see is the swivel chair and table all blended together - the seat and legs of the chair are somehow behind both sets of table legs and the chair's backrest is in front of the table, which doesn't make any sense.
Other mistake: While Sid's toys are working with Woody to get Scud out of the house, just as Hand-in-the-Box is holding the doorknob we can see the screw mounted on the latch's hasp below the loop - which really doesn't make any sense, but as Hand opens the door the screw has suddenly vanished from the hasp and is now properly mounted on the doorway's loop plate, where it's meant to be. If the screw were really mounted through the hasp, the door could not be opened.
Continuity mistake: When Buzz and Woody are attempting to enter the truck towards the end, they ride RC and grab a hold of Slinky to help pull them up. RC loses power and Slinky starts to be pulled onto the road. When he touches the floor to stop him falling he actually pushes against the flow of the road. (01:11:50)
Continuity mistake: Buzz, while pushing the tool box off of the blue basket Woody is in, stretches to about 3 times the length he normally could from that position. When he first starts pushing against the window sill with his feet, he stretches out fully a few seconds later, about half the length of Sid's desk. He continues to push the box over and says "Almost there..." before he does and we can see he still has his feet on the window sill. Most people will have to watch it for a better understanding. (00:59:37)
Other mistake: It's been mentioned that Sid sets his clock for 8:25 and it goes off at 7:00. Here's some more errors for Sid's crazy clock physics. When Woody is saying "Psst" to Buzz from inside the blue plastic basket, the clock on the wall says 6:25, yet the alarm clock next to Buzz says 6:55. It goes off 5 minutes later and after Sid takes Buzz out of the room, the clock on the wall has changed to 3:10. When Woody is talking to Sid's toys a minute later, the clock now reads 10:00. The maximum amount of time that passed between the already wrong 3:10 and the 10:00 is 5 minutes. You can tell because Sid wanted to launch Buzz strapped to the rocket ASAP and Woody wanted to rescue Buzz from his current strapped-to-a-rocket state very fast. (00:56:45)
Continuity mistake: When Sid is setting the alarm clock, he sets it for about 8:25, when the alarm goes off the next morning, it's actually at 8:00. (00:55:42)
Continuity mistake: When Woody and Buzz are at the gas station and the big truck pulls in, Woody falls limp to the ground. The truck pulls over him, and stops with its tires an inch from his head. In fact, the brim of Woody's hat sticks up into the space between the two tires. In the next shot when Woody scrambles out from beneath the tires, his head is directly under the tire to our right. (00:31:40)
Continuity mistake: When the army men parachute down from upstairs, they disappear before the next scene. You see them when they land, but when the other soldiers come down they just aren't there anymore. (00:09:40)
Continuity mistake: When Buzz drops into the van through the sunroof (at the gas station) he has a dead fly stuck to his helmet shield. Woody attempts to pull it off and clean the glass, but doesn't finish the job as there is still some goo on the glass where the fly was. On the following shot the glass is completely clean. (00:30:14)
Continuity mistake: When Andy goes to his room to get Molly, he lowers the side of her crib in order to get her out, picks her up, and walks out of the room. In the next shot of his room, the crib side is back up. (00:03:13)
Factual error: When the soldiers are asked to find out what gifts Andy is getting at his birthday party, the set out down stairs with half of a baby monitor. Well, any parent who owns one knows that there are 2 pieces to a baby monitor. One half (the larger half) is the receiving end (that takes in the noises) and a smaller half which is the transmitting part (the half that sends out the noises). The half that the soldiers take downstairs to talk through is the wrong half. They take the half that the noise comes OUT of. So, really, they should NOT be able to speak into this part - in real life, they'd hear what was happening up in Andy's room. (00:09:18)
Continuity mistake: The blue blanket in Molly's crib repeatedly vanishes and reappears within the same scenes, such as when the batteries are put back into the baby monitor Woody shouts for everyone to return to their positions, in the overhead shot of the room the blanket's gone, but is soon back in its place.