Levicorpus

Levicorpus is one of the more memorable original spells in the books — and another in the long list of Snape inventions recorded in the marginalia of his old Potions textbook. The incantation is non-verbal in its strongest form: a clean wand-flick, no spoken word, and the target is suddenly upside-down in the air, dangling by the ankle as if an invisible hook had caught their leg.

The jinx had a brief but legendary run as a school-yard fad during Snape's own student years. Marauders-era Hogwarts went through a phase, in the late 1970s, of casting Levicorpus on each other constantly — in corridors, in the Great Hall, on the Quidditch pitch — until enough teachers complained and the fad died down. The Pensieve scene showing James Potter using Levicorpus on a teenage Severus Snape, with Snape dangling humiliated and helpless above the lake while a crowd watches and laughs, is one of the more uncomfortable moments in Order of the Phoenix. It complicates James's character permanently.

Harry rediscovers the jinx in Half-Blood Prince by reading Snape's old marginalia, and uses it accidentally on Ron Weasley one evening in the Gryffindor dormitory before figuring out the counter-spell. The cast is, for a sixth-year wizard, surprisingly easy. The counter, however, is its own dedicated spell — Liberacorpus — and a Levicorpus victim cannot generally just shake the jinx off. They hang there, blood rushing to their head, until somebody comes to help them down.

The charm is technically classified as a Jinx rather than a Curse. It does not cause lasting injury and is not Dark Magic in the strict sense. It is, however, deeply humiliating and physically uncomfortable, and most wizarding etiquette treats it as belonging in the category of "funny once, after that it is harassment." The fact that it was invented by a teenage Snape and weaponized against him by a teenage James Potter captures the essential trouble of school-yard magic in one tidy generational loop.