Continuity mistake: When Mr Alfred steps into the dog poo, it is on the front part of his shoe. As he shows this shoe to Preacher, it is now in the middle.
Continuity mistake: Opal's hair style changes significantly halfway through the movie. This in itself is not a big deal, except the character wouldn't do it, they don't have the money to change her style, if they did change her style, there would be reason for it.
Answer: I read all the end credits after the movie and didn't see a listing for "Opal's [AnnaSophia Robb's] Stunt Double", but this does not rule out the possibility that one was used - there could be an uncredited one. In general, a stunt double will be used to perform any of the actor's role that is dangerous or could result in injury or death. This is particularly true for child actors (not legally adults) who must be protected or shielded from danger. Movie producers/directors don't want to jeopardize the health/ safety of any person playing a character and also do not want to have to delay or stop production while an actor recuperates; there are physical and emotional as well as economic harms resulting from injuries. It is best to "play it safe" by using a stunt double. Child labor laws restrict the number of hours per day and the time-frame a child actor may work, so a stunt double or stand-in is often used during the restricted hours to help preserve the child actor's limited time.
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