The first time I took a deer I was sitting on a bucket under an apple tree. The deer ran 50 yards right to me and about 20 yards away just stopped and stared at me. I didn't have a shot because she wasn't turned in the least. I waited for her to turn. And she stared. She stared some more. She cocked her head from side to side thinking, "Hmmmmm. Now what's that? Wasn't here yesterday. Hmmmmm." She kept staring. For an eternity (maybe 2 minutes real time). Now for my part, my gun was aimed right at her and I was absolutely still. I didn't budge. But it was cold and I kept thinking, "She's GOT to see my breath!" Remember, this was my first deer and my heart was pounding and I was sucking wind like you wouldn't believe. Well, eventually she turned broadside and started grazing. I shot her (and her son Bambi when he came running the same trail his momma took, 5 minutes later). So in answer to your question, yes I think they can see your breath, but no, I don't think it matters. They see you and they might even know you're alive, but the "movement" of breath isn't, evidently, as threatening as physical movement. I mean let's face it, you're in the deer's living room and she/he knows you don't belong there.