Several components of a new car may need to be tested long before the body is complete. Many times, engines and drivetrains will be crammed into existing models. These cars are called "mules." The two most famous 2005 Mustang mules were "Chip" and "Dale."

Cars have to be tested before they're released, but manufacturer's have to protect against the competition copying ideas. To accomplish this, they cover the cars with camouflage which makes it difficult for cameras decipher details in the car's design. Photos of these cars are called "spy photos."