Revealing mistake: When Woody falls out of the closet wrapped in the string lights he hears Buzz's voice, and in the next shot as Woody sneaks up to Hannah's room we see Sid's open door and doorway, which looks perfectly normal. However, after Woody rescues Buzz from Hannah's tea party they both stop in the hallway, and there's another shot of Sid's open door and doorway, only this time it's not normal to say the least. Five of the six hasps, bolts, and locks that should be (and normally are) screwed into and attached to the inside of Sid's door (one hasp mechanism, third one down from the top, is attached to the door's frame) are now actually kind of floating there in mid-air right beside the doorway, as if there's an invisible door there. Weird that Pixar artists deliberately did this, but it's bizarrely funny to see.
Revealing mistake: After Helen finds the hair on Bob's suit, she goes to him while he is in the car and says," Have a great trip. I love you, so much.", Bob backs the car out of the driveway. He backs out and turns, but you can see his hand on the top of the steering wheel doesn't move. (00:47:05)
Revealing mistake: When Lightning, Cal and Bobby enter the pit row, the King's model is merged with the one from the crew chief next to him. (00:03:05)
Revealing mistake: In the scene where Luigi offers his service to Van and Minny, Guido is juggling wheels. But when Guido finishes, you can see over his right lift that his one of his wheels is not rendered correctly, as it seems to overstep his bodywork.
Revealing mistake: When Mater and Holley are talking in the corridor, Mater's reflection is cast on the wall, but Holley's reflection isn't. (00:29:55)
Revealing mistake: When the toys are watching Woody being stolen the games machine on top of the TV doesn't have its controllers plugged in, but Rex was playing earlier with a wire coming out of his controller, which clearly wasn't actually connected to anything.