Vibration. That's pretty much it. You feel your throat vibrate when you speak. You can also hear your voice resonate through your head, and it's well-known that people are often surprised when they hear their voice on a recording, because that resonance alters the sound, and most people don't realize what they sound like until hearing their voice on a recording of some kind. Also, a lot of people tend to fumble over their words more than most. This can be caused by a condition (like stuttering), or it can just be due to thinking ahead of yourself. I do that occasionally. That, or I pause partway through a sentence and start saying "uh, um....uh" because I have mild ADD and occasionally lose focus on what I'm saying.