He seems to be savoring her moment of wonderment, and answers after a moment, "it's called energon. Some of those tall, metal people use it as food and currency. It is... potential energy, crystallized in great density in a form easily converted to whatever other form is needed." He gestures invitingly, adding, "it's quite safe to touch."

The cube is faintly warm, and hums just a little bit, inaudibly.