I take this articole on the net.
"The quills of crested porcupines serve as an effective defense against predation. When disturbed, they raise and fan quills to create an illusion of greater size (Nowak 1991). If the disturbance continues, they stamp their feet, whirr quills and charge the enemy, back end first, attempting to stab with the thicker, shorter quills (Nowak 1991; Grzimek 1990). Such attacks have been known to kill lions, leopard, hyenas, and humans (Nowak 1991)."