This is called a 'hunger puke', acid reflux or bile vomit. Dogs and cats naturally have very acidic stomach conditions (which aid effective digestion and catalysis of meats and bones; and act as a protective measure against pathogenic bacteria). When reverting to their natural diet - a raw diet - their bodies return to their normal acidic state (compared to kibble and other commercial diets which induce a relatively unhealthier, alkaline internal system). If the interval between dinner and breakfast time is too long (i.e. more than 13 hours), or if your pet doesn't get solid sleep through the night, owners may find themselves with greeted with a foamy, yellow, pink, or green puddle in the mornings. Some simple solutions: make dinner times later or breakfast times earlier, or both; and try to ensure your pet has a nice quiet place to sleep at night!