Are You In Love

Are you in love? That is an interesting question. People ask each other that every time and are expecting an answer to be yes or no. But how do you know if you are in love? I mean many have said already..."you just know". But how? Is there a hint, a clue, or what? How do you determine that you are in love with this other person? Is it by how s(he) looks like, smiles, walks, talks, does certain things? The way they lead their life? How do you know that you want them to be in your life because you are in love with them? Can anyone explain that???