The easiest way is to cut the mushroom open. A true morel is completely hollow inside. False morels are stuffed inside with a cotton-like material. The second key to identification is how the cap is attached to the stem. A morel cap is attached to the stem at the bottom of the cap. False morels cap is connected to the stem at the top of the cap. Just to make life confusing, though, there are two half-free true morels with caps that attach to the stem half-way down. This is still different from false morels so it shouldn't be too confusing.