When Hagrid brought Harry to Diagon Alley for the first time, Harry heard a woman say "Seventeen sickles an ounce for Dragon Liver. They're mad." But Hagrid told Harry that there were seventeen sickles in a galleon. So that would be like saying "100 pennies" instead of a dollar.

In 'Through the Trapdoor' in book 1 Harry, Ron and Hermione take the place of the chess set pieces. Ron takes the place of a knight but when it comes to him sacrificing himself to the queen he only takes a pace forward. Knights cannot move just 1 pace forward.

Harry buys the book "One Thousand Magical Herbs and Fungi", but later in the book it says Harry looked up 'dittany' in "One Hundred Magical Herbs and Fungi."

Aunt Petunia says that Lily would "Come home every vacation with her pockets full of frog spawn, turning teacups into rats." but according to ministry rules, this is illegal. If she did this in her muggle home she would most likely be expelled as Harry almost was.

In book 1, it is almost Nearly Headless Nick's 400th deathday. But in book 2, he celebrates his 500th deathday.

In the first book it said that by drinking the Elixir of Life it would make the drinker immortal, but later in the story Dumbledore says to Harry that the Flamel's had enough Elixir stored in them to set their affairs straight. But if by drinking the Elixir of Life makes you immortal then you would never die.