An electrical current as small as 6 mA passing across the human heart can be lethal, while any electric current above 1 mA is at least painful, if not lethal. The "path" from one arm, across your chest, to your other arm typically has a resistance of 10,000 ohms, and if you grab two electrical terminals - one in each hand - the resulting current will usually travel up one arm, through your chest, and down your other arm. So if you were to grab a 12 V car battery by each terminal (again, one in each hand), what would happen?