其 is strong for KI. So you can say,
THAT animal's EYES and LEGS are the KEY to its survival (Talking about chameleons here. Fuck changing colors and catapult tounges - prehensile suction-legs and 360-vision eyes are what really makes those little goons such ruthless predators)
(Actually that was kind of a long detour for an at-best passable mnemonic, but) (actually there is no 'but, since chameleons are THE BEST SHIT)