Popeye, the Sailor’ cartoons taught children that eating spinach boosts strength and helps defend against bullies. Lötscher and colleagues report that dietary deficiency of magnesium ions (Mg²⁺), against which eating spinach is an excellent antidote, impairs the activity of a key adhesion molecule, LFA-1, and hinders the ability of CD8⁺ T cells to grapple with assorted bullies, such as tumors and bacteria.