Factual error: When Harry talks to the snake, the camera shows a close up of the snake, and it blinks. Snakes don't blink because they lack eyelids. (00:06:50)
Factual error: The Hogwarts Express leaves from platform nine and three-quarters, between platforms nine and ten at King's Cross station, London. The platforms shown in the film as nine and ten are, in fact, four and five (the only platforms that have a wall between them as shown in the film). The real platforms nine and ten are in a separate part of the real station. In addition, when Hagrid and Harry are on the footbridge, they are walking towards platform one, away from both the real platforms 9 & 10 and the film's platforms 9 & 10. No wonder Harry feels lost when Hagrid leaves him to find the train on his own! (00:31:55)
Factual error: When Hagrid visits the Dursley family in the hut on the rock, Hagrid grabs and bends the shotgun barrel while it is still being held by Mr. Dursley. This is impossible. The gun is made of strong metal, and when Hagrid grabs it, it starts bending, while still in Dursley's grip. Seeing as how Hagrid (the half Giant) is very strong, he should either knock Dursley to the floor or pull the gun straight out of his hands (and maybe his arms with it), if Dursley were to really keep hold of the gun as it is bending. Mr. Dursley must have one strong grip. (00:13:35)
Factual error: The first film takes place from 1991-1992 (the seventh film shows James and Lily's grave, with the correct dates to have the film take place in 1991), however when Harry asks to borrow Ron's Daily Prophet during the first mail delivery, the date at the top reads 2001. (00:52:30)
Answer: Petunia or Vernon would have ran to a zoo employee and told them what happened. The employee would then open the door to the snake exhibit letting Dudley out.