Morsmordre is the incantation of the spell used to conjure the Dark Mark, the skull-and-serpent sign used by Voldemort and his Death Eaters. It is very likely that Voldemort invented this piece of magic and taught it to his followers. Only Death Eaters and Lord Voldemort know the correct way to cast the spell, although Horace Slughorn is implied to know how to cast the spell as well. Death Eaters often cast it after committing a murder, placing the Dark Mark in the sky over the location of the victim's corpse. It is against the law to cast this spell, even though, beyond its symbolic impact, there's no indication the spell causes any physical damage.
"The Buddha is saying, ‘You are this.’ He doesnt say, ‘I have something extra that I am going to give you.’ Trust in yourself, trust in who you are. Sit down, breathe, be listening right now, hearing right now. Be intimate. But you have to do it for yourself."
Elihu Genmyo Smith, “No Need to Do Zazen, Therefore Must Do Zazen” (Via Tricycle Daily)