The nundok in nundok deurida means the charged force of a gaze brimming with greed. The dok here is not so much venom like a snake's as the thick, sharp intensity that hangs in a stare fixed hard on something. In Korean, a powerful working of the mind is often expressed as dok. When you want something so badly that your heart leans toward it, the first thing to change is your eyes: you cannot tear them off the object, and you keep glancing at it, watching for a chance. To "set" (deurida) that covetous gaze upon a target is precisely nundok deurida. So the phrase means not merely looking, but watering at the mouth with want and biding your time to seize the thing.