2. Real numbers $x, y, z$ are chosen such that the numbers

$$
\frac{1}{\left|x^{2}+2 y z\right|}, \quad \frac{1}{\left|y^{2}+2 z x\right|}, \quad \frac{1}{\left|z^{2}+2 x y\right|}
$$

are the lengths of the sides of a (non-degenerate) triangle. Determine all possible values of the expression $x y+y z+z x$.

(Michal Rolínek)