  This paper is aimed at pursuing a recent discussion about the comparison
between Self-Organised Criticality, the jamming process and the percolation
theory in the problem of a silo discharge [I. Zuriguel, A. Garcimartin, D.
Maza, L.A.Pugnaloni, J.M.Pastor, "Jamming during the discharge of granular
matter from a silo", Phys.Rev.E 71, 051303 (2005)]. Statistics of blocking a
silo is investigated from different models: percolation, self organised
criticality..
