From Halopedia, the Halo wiki
The energy garrote is a Covenant weapon used by Special Operations Sangheili. It is a small two-piece cylinder that splits apart in the middle, causing a green arc to form between the pieces. Much like a typical garrote wire, this arc is used to choke and burn an enemy quietly from behind.
The energy garrote was used during the Battle of Installation 04 by Zuka 'Zamamee to kill Rick Hale, the pilot of a D-77 Pelican dropship. 'Zamamee took control of the craft and landed it and its complement of Special Operations Sangheili at the Human Alpha Base on Installation 04.
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