Invisible gas which apparently knocks people unconscious.
Fred and George were planning to release Garrotting Gas in a corridor, but left school before they had a chance to carry out the plan. Ginny seized upon the idea as a diversion to keep Umbridge away from her office. NOTE: 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 (OP32).
Cut ginger roots are used in Wit-Sharpening Potion.
Powdered horn is used as a potion ingredient (FB)