The Marauder's Map shows "every detail of the Hogwarts castle and grounds" including the location of everyone at the school.

After betraying James and Lily Potter to Voldemort, Peter Pettigrew, an animagus, turned himself into a rat and lived as the Weasley's pet for over 12 years.

During her third year, Hermione used the Time-Turner to relive hours over again so she could do several lessons at once.

The Whomping Willow was planted to protect the secret tunnel into the Shrieking Shack. Remus Lupin would use the Shrieking Shack to have a safe place to turn into a werewolf when he was a student at Hogwarts.

Dobby, trying to keep Harry from "mortal danger" at Hogwarts, causes Harry to be locked in his room at the Dursley's, miss the Hogwarts Express, and break his arm during a Quidditch match.

Harry casts a Patronus in the shape of a stag, the same as his father's.

Nagini is a giant snake that is also one of Voldemort's horcruxes.

Wizards travel using a variety of methods including portkeys, floo powder, and apparition. Aparecium is a spell to make invisible ink appear.

A house elf can only be freed if their master presents them with clothing. Harry gives Lucius Malfoy Tom Riddle's diary wrapped in a sock and Lucius throws the sock aside. Dobby catches the sock which sets him free.

While they dated, Lavender's pet name for Ron was "Won-Won".