Sentence:  At work Mr. Burns spies Homer <WSD>munching</WSD> complacently on a donut and hisses that each donut Homer shoves into his fat face brings him one donut closer to the poisoned donut Mr. Burns has ordered thrown into the mix as a form of culinary Russian Roulette, only to learn from Smithers that the plant's lawyers ultimately nixed the poisoned donut plan because “they consider it murder.” 
Meaning of the word marked with <WSD> tags:  To chew with a grinding, crunching sound, and with the mouth closed &mdash; often used with "on".