Severus Snape's doe Patronus in Harry Potter revealed that he had been in love with Lily Potter and was the one who helped Harry find the Sword of Gryffindor, but its meaning went far deeper than that. The moment the professor showed Albus Dumbledore the form of his spectral guardian is among the most iconic scenes of the Harry Potter series, especially paired with actor Alan Rickman's emotional delivery of the simple line "always." However, the context of the books reveals how the scene of Snape's Patronus reveal contained several layers of symbolism and heavily impacted Harry's story.

Harry first learned about Patronuses in Harry Potter and the Prisoner of Azkaban, but the movies simplified the explanation of how this spell worked. Only truly talented wizards could produce a fully corporeal Patronusmost could only emit a silvery mist from their wands. Moreover, a wizard could not choose the form their Patronus would take,...