Personally, I know I'm horny when I find myself wanting to think about sex, and then when I do think about sex, my body and my brain both respond with arousal. My brain goes, "Fuck that's hot, think about it some more," and my body gets turned on. And it's kind of a feedback loop; my brain being turned on gets my body turned on, and then my body being turned on makes my brain more turned on, and so on.

When I'm not horny, I don't have that much desire to think about sex, and when I do think about it, my brain just kind of goes, "Ok, so?"

Horniness is what turns a sexual thought into something hot. When I'm not at all horny, I can think about the porniest things and...they're just things. Like my brain just goes, "Yup, a penis can go into a vagina, that's a fact that is true."