\[ \begin{pmatrix} z \\ y \end{pmatrix} \]
is an eigenvector corresponding to a real eigenvalue of the matrix\[ \begin{pmatrix} 0 & 0 & 2 \\ 1 & 0 & -4 \\ 0 & 1 & 3 \end{pmatrix} \]
then \( z - y \) is equal to .................\[ A \begin{pmatrix} z \\ y \end{pmatrix} = \lambda \begin{pmatrix} z \\ y \end{pmatrix}. \]
\[ \begin{pmatrix} 0 & 0 & 2 \\ 1 & 0 & -4 \\ 0 & 1 & 3 \end{pmatrix} \begin{pmatrix} z \\ y \end{pmatrix} = \lambda \begin{pmatrix} z \\ y \end{pmatrix}. \]
By solving this system, we find that \( z - y = 0 \).\[ \boxed{0}. \]