Helioskrill

Helioskrills are predatory creatures that live on Sanghelios. In order to feed themselves, they remain completely still at a location, imitating a rock, waiting for unsuspecting prey to pass by. There is Sangheili stance modeled on the Helioskrill's hunting position. It allows the performer to appear to be resting, but actually allows the user to be ready to spring to their feet in a matter of less than a second. The user must have a certain amount of stamina, however, because it can cause the muscles in your legs to begin to burn. Thel Vadamee' used this position whilst being held in a cell by humans in the Rubble with three other SpecOps Elites.

Trivia

 * Their name, Helioskrills, suggests they are from Sanghelios even to those with limited info.