A porcupine does not shoot its quills at danger as was previously thought but instead the quills pierce the skin of the intruder and overlapping scales on the tip lodge like a fishhook making them difficult to pull out. New quills grow in to replace lost ones.
I have observed lions and leopard that have had quills lodged in the faces. This can lead to the death of the predator if the quill is in a place that prevents it from feeding - and the quills may fester.
Porcupines will warn predators by rattling quills on the end of the tail. If this does not work the porcupine will reverse into its attacker, lodging quills in the predators face.
I observed two lionesses attempting to hunt a porcupine and its' young. In a bid to protect its young, and itself, the adult would always move its back side to face the lions. The cat and mouse went on for more than an hour before the lions gave up.
The Porcupine, Africa's largest rodent, feeds on roots, bulbs, tubers and tree bark and it is thought that porcupines chew on bones for calcium as the burrows often have bones lying around.
Very little is known about the breeding of porcupines, but what is certain is that the young are well developed and the quills harden within the first few weeks.