A porcupine has the pricks on the outside.
Attire
One goes from black to white, the other goes from white to black.
Because it's easier to deal with just one prick
A prick
The pricks are on the outside of a porcupine
A lightbulb.
BMWs have the pricks on the inside!
The pricks are in the inside of the Porsche.
A: The porcupine has the pricks on the outside.
Optional.