When Harry, Ron and Hermione are camping and they get caught by the Snatchers, Hermione pretends she is Penelope Clearwater, apparently a Muggle-born, having been Petrified by the Serpent of Slytherin in Harry Potter and the Chamber of Secrets. Furthermore, Cornelius Fudge later stated that there were "four attacks on Muggle-borns."
Near the end of chapter thirty, it says that the only people left in the Room of Requirement are Harry, Ginny, Mrs. Weasley, Lupin, Fred, George, Bill and Fleur. But on the next page Percy (who had recently entered the room) apologises to Mr. Weasley, but Mr. Weasley had left the room along with all the other people.
When Harry is viewing Snape's memories, he witnesses a scene on Platform 9¾ between his mother and Aunt Petunia, in which Petunia tugs her hand out of Lily's grasp. Her hand is then back in Lily's and she tugs it out again. Similarly, if Petunia had been on Platform 9¾ before, she should have known where it was and been able to tell Vernon, though given her nature, it is very likely that she simply chose not to out of spite.
When Harry talks to Griphook about breaking into Gringotts, Griphook has the Sword of Gryffindor in his hands. When Harry stands up to leave a few moments later, the sword is now beside Griphook's bed.
At the beginning of chapter two, it says that Harry cannot use magic due to not coming of age for 4 days. In chapter six, days have passed since the Battle over Little Whinging, but Harry states the Trace will break in 4 days.
When Harry, Ron, and Hermione leave the Great Hall after the Battle of Hogwarts ends, Harry is under his Invisibility Cloak, and remains under it when they reach the Headmaster's office. When Harry raises his arms to silence the headmaster and headmistress portraits, he is suddenly visible to everyone, but there is never any mention of him taking the Cloak off.
When Harry, Ron and Hermione are at the front door of Xenophilius Lovegood's house, Hermione says to Harry, "You better take off the Invisibility Cloak, Harry, it's you Mr. Lovegood wants to help." and he handed her his Cloak to place in the beaded bag. But later after the Death Eaters arrive Hermione says "Harry give me the Invisibility Cloak, Ron, you're going to put it on."
In chapter Twenty-three, Narcissa says that Draco "is home for his Easter holidays." In chapter Twenty-four, the sun is described as rising at Shell Cottage in Cornwall. But shortly after this, Harry sees into Voldemort's mind at Hogsmeade, where it is "still dark, because it was so much farther north." But (in the absence of a significant longitude difference, as in this case) this sort of thing is only true between the Autumnal and Vernal Equinoxes; Easter occurs after the Vernal Equinox[4] (e.g. on April 12 in 1998), in the other half of the year when sunrise is earlier the further north one goes, thus it should not have been dark at Hogwarts when Harry saw into Voldemort's mind.
In Chapter 27 Harry drips dittany through the singed hole in his jeans to the angry burn beneath. But he has just got changed, so he shouldn't be wearing his singed jeans anymore.
Voldemort's unintentional Horcrux should not even have been possible due to Lily's protection within Harry's blood. If Lily's love for her son protected Harry from any part of Voldemort being able to touch him, the bit of Voldemort's soul should not have been able to touch Harry — much less live inside him for nearly 17 years.
When Harry, Ron, and Hermione break into the Lestrange's vault at Gringotts in Chapter 26, Hermione performs a whispered Levicorpus spell on Harry so he can reach the Horcrux without touching the other contents of the vault. The Levicorpus spell, however, is most effective as a nonverbal spell, which Hermione ought to have known given her talent.
