Locomotor Mortis

Locomotor Mortis — the Leg-Locker Curse — is the school-corridor classic that nearly every Hogwarts student has had cast on them at least once. The incantation is dog-Latin: locomotor (movement) + mortis (death, broadly), translating roughly as "motion-arrested." The cast snaps the target's legs tightly together at the knees and ankles, and any attempt to walk produces an awkward hop or, more often, an outright fall.

Harry's first encounter with the curse is on the receiving end. In Philosopher's Stone, Draco Malfoy hits Neville Longbottom with Locomotor Mortis in a corridor, and Neville has to bunny-hop the rest of the way to the Gryffindor common room before Hermione can find the counter-spell. The scene is small but it sticks — partly because it captures so cleanly what makes the curse so unpleasant. The victim is not in serious pain. They are simply rendered ridiculous, and the embarrassment compounds with every hop.

The counter is the standard Finite Incantatem. Some particularly strong-willed wizards can shake the curse off after time, especially as the caster's concentration fades, but most have to wait for help. In serious applications — Death Eater detentions, dark-corridor encounters — Locomotor Mortis can be combined with other curses to immobilize a target for capture, though for that purpose Petrificus Totalus is generally considered the more reliable choice.

The curse sits firmly in the curriculum's middle tier — taught at Hogwarts as a standard practical jinx, used commonly enough in school-corridor duels to be recognizable to anyone, and still not treated as Dark Magic. Like most spells in this category, the line between prank and bullying depends entirely on context and intent.