  Restricting the functional integral to the Gribov region $\Omega$ leads to a
deep modification of the behavior of Euclidean Yang-Mills theories in the
infrared region. For example, a gluon propagator of the Gribov type,
$\frac{k^2}{k^4+{\hat \gamma}^4}$, can be viewed as a propagating pair of
unphysical modes, called here $i$-particles, with complex masses $\pm i{\hat
\gamma}^2$. From this viewpoint, gluons are unphysical and one can see them as
being confined. We introduce a simple toy model describing how a suitable set
of composite operators can be constructed out of $i$-particles whose
correlation functions exhibit only real branch cuts, with associated positive
spectral density. These composite operators can thus be called physical and are
the toy analogy of glueballs in the Gribov-Zwanziger theory.
