I have read that it often feels like a tingling sensation. It can happen in both breasts at once, because sometimes the breast you're not nursing on will still let down and leak a little. And hearing your baby cry or thinking about him can trigger letdown as well. (I thought this would never happen to me because I don't think of myself as a very emotional or textbook person. Then my LO cried in the other room and I looked down to see two large wet spots on my shirt!) But I've also read that it's very normal not to feel anything. So far, I don't feel it at all, but I can tell when it's happened by the type of swallowing Haley does, and often I can see milk at the corners of her mouth.