We have had the gagging, then the watery-mucusy vomit a few times. Though only for the first few weeks of BLW. Hasn't happened in a while now (over a month). One day when it happened I had a friend over who is a doctor (General Practitioner) and he said it is exactly the same as possetting (ie. what babies do when they bring up some milk after a breastfeed). He said it is entirely normal and nothing to worry about.