Take a 9V battery (that's, oh lets see... 3V less than a 12V car battery) and touch it across your tongue. Your tongue has far less resistance than any external organ, like, say, those suggested in the parent. It'll tickle and might even not be comfortable, but it won't hurt. I'll skip the test you suggest but probably for reasons other than you might think. Thanks for the compliment, but it doesn't really take a genius to know this stuff--just ohm's law and a little experience with batteries, multimeters, etc.

While the alligator clamps may hurt, 12 volts isn't enough to cause you to even notice.