Board Thread:Speculation House/@comment-50.108.101.248-20171026123354/@comment-26397825-20171026124634

It is a really odd thing to think about; the Grimm do have eyes and they do appear to use them. If they didn't use them at all, how would they know where to find a human that is not feeling a negative emotion at that particular time? Huntsmen wouldn't go into a fight feeling fear and anger and depression; they'd be determined more often than not and yet Grimm can still see and track them in a fight.

Personally I think they detect negative emotion sort of like a radar, in that they can feel the general location in comes from but not use it to pinpoint the exact location except through manually searching. A sudden intense spike of negative emotion attracts their attention away from people who are not feeling such intense negative emotions (such as Ruby's fear towards the Ursa in the V5 Yang Character Short), but it is not the only way they see things. I think that their eyes do work and they can use them to locate humans and attackers.

Following on this, I think that Ren's semblance works as a sort of perception filter system towards Grimm; it's unclear if it hid Qrow and Jaune from Ruby and Nora but Ren was able to see them since it is his semblance. Basically it makes it so the Grimm can't perceive them through either sight or emotion sensing.

I do think a smoke screen/blinding a Grimm would work to a degree, but they do have ears and can sense tremors in the ground (such as when Weiss hit the floating island the Queen Lancer was on, which woke it up). This plus the negative emotion sensing does still give them a range of ways to detect people, so merely blinding them wouldn't render them completely insensate.