What's the difference between a porcupine and a BMW? Porcupines have their pricks on the outside

What is the difference between a BMW and a porcupine? On a porcupine, all the pricks are on the outside!

There are hundreds of features on a brand-new BMW; heated seats, bluetooth audio, laser-headlights, etc... Which among them goes completely ignored? The turn signals.

What's the difference between a BMW and a porcupine? In a BMW, the prick is on the inside.