All babies are born with a loose muscular piece of tissue between the esophagus and stomach that tightens up over the first 6 months of life. As a result, milk goes down...and milk comes up. Hence the perpetual spit up, and burp cloth draped over every new parent's shoulder. When the milk comes up, it sometimes comes out of the mouth as spit up, but may also come up behind the nose since the mouth and upper airway are all attached. When milk goes behind the nose, a baby will sound kind of snotty. It's not snot, though, it's milk. No worries!