The Russulas are notoriously difficult to ID. Some are choice edibles, but others will definitely make you sick. There are dozens if not hundreds of very similar looking red russula mushrooms all over the world. The only other technique I'm aware of to narrow down what they may be is to bite off a tiny corner of the cap, chew it for a few seconds, and then spit the flesh out. Some red russulas are bland tasting, but others are spicy (almost like cayenne pepper). If I'm not mistaken, the spicy taste is more closely associated with the species known to cause gastrointestinal distress.