Hi there, Because of the unique anatomy of the rabbit's digestive tract, they are not capable of vomiting in the same way that other species can. When we see what looks like vomiting, it's likely that what is really happening is that there is a blockage in the esophagus and mucus and saliva that the rabbit would normally swallow (which is often green/brown due to their normal diet) comes out. They produce a LOT of this material, since what they normally eat is dry and fibrous, so it can be quite impressive to see. Sudden diarrhea, when your rabbit has not had diarrhea recently, can be a stress response to the discomfort of having a blocked esophagus. If this is the case, it sounds as if your bunny was able to pass the offending item (which could be a big bite of food or a wad of hair from grooming) by himself. I'd recommend continuing to monitor him and feeding him in small amounts to make sure he chews and swallows fully for the next few days. If you see continued diarrhea, I'd recommend a trip to the vet for a full exam to make sure he doesn't have other reasons to have diarrhea, but it sounds as if he will be fine with a little careful watching. Also, if he breathed any of the mucus you saw around his mouth, he may be more likely to get pneumonia/respiratory infection. If he is behaving abnormally, hiding, not eating, or having trouble breathing in the next week or two, he should visit a vet and be treated with antibiotics.