Uncle Vernon and aunt petunia kept looking at each other darkly."

Give two reasons why these characters look at each other darkly based on what you have read in this chapter? Harry Potter book.

In this passage, Uncle Vernon and Aunt Petunia exchange these looks due to the context of the situation: they are the non-wizard guardians of Harry, who is receiving letters of acceptance to wizarding school. Uncle Vernon and Aunt Petunia strongly disapprove of the wizarding world and magic, so their "dark looks" come from a place of fear and dread that Harry is being invited into that world. This can also be attributed to the fact that Petunia's sister (Harry's deceased mother) was a witch, so they saw her involvement with magic as a corrupting force that led to her doom. Their dislike of magic is therefore one reason, but another reason is that they already strongly resent Harry's presence in their house. They often abuse and neglect him, so the recurring letters is a source of frustration because it makes it very difficult for them to ignore the issue of Harry becoming a wizard.