What exactly happens when electricity flows through a person, how does it effect their body and how can these effects be measured?
People are conductive, electricity will flow through a person if able, and can do harm to a persons body, including burns and upsetting the heart. Small enough voltages might not conduct through your skin, the most susceptible place on your body is probably your tongue.
In terms of Amps, 1 mA of current through your body would only cause tingling, but upwards of 75 mA could cause ventricular fibrillation, an unsteady heart rhythm that can lead to death. Amps of 1500 mA can start to burn internal organs. However amperage alone cannot determine whether a shock is deadly, factors like where the current flows through on your body are important too, this is why a small shock from an electrical shock can kill you if it travels through your heart, but a bolt of lightning can leave a person with only burns if it travels through the skin and into the ground.