Slugulus Eructo

Slugulus Eructo is one of the more notorious curses in the wizarding canon, and it occupies an unusual position in extended-canon history. The book version of the famous slug-vomiting incident in Chamber of Secrets — Ron Weasley using his broken wand on Draco Malfoy in defense of Hermione, the spell backfiring catastrophically, and Ron spending the next several minutes hunched over a bucket of Hagrid's outside his hut — never names the incantation aloud. The spell is described, vividly, but the words Ron tries to cast are not given on the page.

The incantation Slugulus Eructo, however, is established in extended canon — most prominently in the Chamber of Secrets and Half-Blood Prince video games — as the spell behind Ron's misfire. The Latin reads roughly as "slug erupt," which is plain-spoken even by spell-curriculum standards. People have searched for the spell by name for decades, which is why most encyclopedias of wizarding curses (this one included) carry it under the extended-canon label rather than the strict book one.

The cast itself, when it works, forces the target to vomit slugs continuously for several minutes. The slugs are real — slimy, alive, and unpleasant to clean up — and the experience is universally described as one of the worst things a witch or wizard can have happen to them. The duration is usually short, the lasting damage is essentially zero, and the embarrassment is permanent.

Ron's specific case is complicated by the broken wand. The cast fired backwards along the wand's broken core and struck the caster instead of the target — Hagrid's bucket scene captures the consequence. The spell also serves, in retrospect, as one of the early signals that Ron's wand really does need replacing, a thread that runs all the way to the wand's eventual destruction at the lake in Prisoner of Azkaban.