Bad insulation on a live wire. Where in the engine bay?

 

Then only voltage high enough to make you feel it by touch is produced at the ignition coils and the HID lights.

 

Right. It always makes me laugh when I see TV or movie where they are using a car battery to torture someone. A battery by itself can't hurt you (unless you drop it on your foot, drink the battery acid, or overcharge it to produce hydrogen gas and ignite it).

Everything in the car uses harmless 12v or less, except for the mentioned ignition coils and hid lights.