Final answer:
A shock greater than 5 mA can cause muscular contractions, with currents from 10 to 20 mA causing an involuntary "can't let go" effect. Extremely high currents of 100-300 mA and above can lead to ventricular fibrillation or burns, possibly resulting in fatality.
Step-by-step explanation:
Concerning what a > 3 mA shock can do to a person, very small currents, typically less than 1 mA, go unnoticed and are harmless. However, once the current exceeds 5 mA, the potential for harm increases. At currents from 5 to 30 mA, a person may experience sustained muscular contractions similar to nerve impulses.
More notably, at the "can't let go" threshold of around 10 to 20 mA, the muscles in the hand can involuntarily grip the electrified object, potentially prolonging the shock. This involuntary grip can be dangerous both to the victim and to anyone attempting a rescue.
At much higher currents, from 100 to 300 mA and above, the person can suffer from ventricular fibrillation, burns, or both, depending on the concentration of the current. Ventricular fibrillation can be fatal as it disrupts the heart's electrical patterns, leading to ineffective blood circulation.