Magical effects
Dumbledore's Army Hogwarts Shops and merchants Wizarding Culture

Garroting Gas

"Luna and I can stand at either end of the corridor ...and warn people not to go down there because someone's let off a load of Garrotting Gas. ...Fred and George were planning to do it before they left."

-- Ginny Weasley (OP32)

Commentary

Etymology

Kill (someone) by strangulation, especially with a length of wire or cord (Oxford Dictionary)

Notes

It seems highly unlikely that Fred and George would have released something which was actually deadly, so we assume that Garrotting Gas is non-lethal

Pensieve (Comments)

Editors: and