How do porcupines defend themselves?

Hint: The name porcupine is given to the creature due to the numerous spines it possesses. These spines are known as quills which have sharp barbs on the terminal ends. These spines are modified body hairs that have been hardened and they are covered with keratin.

Complete answer:
-When a porcupine senses danger near it, it coils upon its belly and erects its quills, bristling and protruding outwards. The quills penetrate the skin of the enemy and the barbs present on the top of the quills hold it inside the enemy’s skin.
-The tip of each quill has a tiny rear-facing spike, which means the quills can easily penetrate the surface but are hard to remove because of their hook shape. The quills then release themselves from the porcupine's body and stay attached to the enemy. This causes tremendous pain to the enemy thereby distracting it. These quills are difficult to remove as well because of the barbs. The porcupine takes advantage of the situation and escapes from the enemy.
-This is a porcupine's best defense mechanism - when the spines penetrate the skin of the enemy they are not only very painful but also difficult to remove.
-An important feature of these spines that are called "quills" is that when they are released they can easily penetrate the skin of the enemy. There they get stuck easily but are very difficult to remove.
Also, when the porcupine is ready for action, it moves its body and shakes it purposefully. The quills rattle against each other and make a menacing metallic sound.
-Therefore, informing the predators that a porcupine is somewhere near.

Note: It has always been said that porcupines can shoot their spines out, but this is not true.
However, porcupines can release their spines after they have penetrated the skin of the enemy.
Porcupine spines are very important in the defense and attack mechanism of animals.