How do zombies detect "food"?

[Gorn Captain]

I was wondering, do they use their senses as we do?

In early Walking Dead, we see Rick and Glenn coating themselves with walker guts to avoid detection.
So the rule would be "smell"?
Michonne uses "neutered" walkers to blend in. But they walk at a distance from a couple of feet. Yet other walkers (even ones a foot away from her) don't detect her until she starts moving faster and beheading some.
So in this case, it wasn't just smell, but also motion.

Do they use sight then, as they react to motion?
Can they actually use their eyes, as these are the first to rot and deteriorate?

Also, why do Michonne's neutered walkers stop "getting an appetite"?
Yes, they have no arms or lower jaw, but that shouldn't stop their hunger. Why do they leave her alone, and don't even attempt a "nibble"?

[johnmiic]

I prefer the Romero films where it seems more mysterious. They just seem to know, (tho motion and noise can bring them out on you). In Walking Dead smell, noise, motion seem to work. Also remember back in season 1 how Glen was talking to Rick and one seemed to eye him suspiciously until he started moaning instead of talking. Tho there does seem to be a range limit. If you're just far enough they don't detect you. Still that varies from walker to walker.

[YoungOnce]

I'm guessing that Michonne figured out that whatever makes walkers crave human flesh is located in either the lower jaw or the arms. By hacking those off, they seem to no longer have the urge to eat her.