I believe that the answer lies in something profoundly simple, and that's the "space between the electrons", or the Universal Energy that connects us all together. How is it that you "sense" someone is bad just by looking at them or getting close to them physically? Perhaps your energy body is reading their energy body and realizes that there's something not not quite right with them. You pass them, your dog growls at them for seemingly no reason, and you get the heebie-geebies. You wonder if that person is a child abuser and you can't even believe you're thinking it! Or you meet another person that you just instantly like and you want to be their friend. I think that you are simply finding a person who is vibrating at your frequency, or even higher, and it "feels" good to be around them.
Obviously there's the eye contact, the handshake, the way the person is dressed or even how they smell that affects you. But there's got to be more to it than that. Or I couldn't do what I do as effectively as I do. My clients will tell you that I "see" their passed on relatives without having ever met them, that I visualize events in their lives that I could not have possibly known about, that I sense/see and even smell things that go on with their animals and can articulate them very accurately. It's not a parlor trick; it's a way of communicating on a very subtle level using the soup of Universal Energy that connects us all; the "space between atoms" that spins and vibrates with a frequency that gives information to those who are tuned in and willing to listen.
Foster Gamble of THRIVE fame articulates this concept very nicely in this short video that will get you thinking about that Universal Energy soup and how we might be connected in ways that our normal five senses don't detect.