https://www.seattlepi.com/news/article/Car-Talk-Car-battery-...
EDIT - here's some math:
The U.S. Navy FIRE CONTROLMAN Volumes 01 - 06 & FIREMAN gives 1500 ohms as a common resistance approximation between extremities, either hand to hand or hand to foot, for an average human body.
I = V/R = 12V / 1500 Ohms = 0.008 A
8 mA is not nearly enough to kill you.
But sure, it's probably best to not touch the car battery terminals when your hands are bleeding.