There are many types of mushrooms that are toxic. Depending on the species of mushroom that toxicity can be express as something as simple as transient vomiting to convulsions and death. Proper mushroom identification is difficult as there is overlap of many identifying characteristics. For example there are small red mushrooms that are not toxic and some of the deadliest mushrooms are small and red. You can check with a county extension office or the mycology dept. of a nearby university and they may be able to help you with correct identification. If transient vomiting in a dog that otherwise feels ok is all that you see there shouldn't be a problem. If any other symptoms please contact you veterinarian.