Need a little help.....I have a one month chick that is not thriving like her sisters. For the past couple of days I have been hearing a gurggling sound in her crop area. Last night I massaged her crop and she vomited a lot of foam. She is eating, drinking and pooping but is about the half the size of the others. She is eating starter feed, grit is available for all of them, water has ACV mixed in it as well. Any suggestions on what the foam could be? I have dealt with sour crop in an older chicken and have no reason to think that is what this is. She has never eaten grass or anything other than starter feed.