While I have read on Walking Dead Wiki http://walkingdead.wikia.com/wiki/The_Walking_Dead_Wiki that walkers do not have to eat the flesh of the living to continue to move, and function (as they are already dead), that the impulse to eat the flesh of the living is their strongest impulse. Eating the flesh of the living does seem to energize the walkers…this guy, You Got A Little Something On Your Face, There, Buddy Walker does seem infused with some vim and vigor after chomping on some poor somebody, or some thing.