At the beginning of the experiment, the test subject would be given a quick shock from the apparatus on its lowest power level. Milgram included this to ensure the subject knew how painful the shocks were; to make the pain of a shock “real” to the subject before proceeding.
As the experiment got underway, the administrator would give the unseen confederate a series of memorization problems requiring an answer. When the confederate gave the wrong answer, the administrator would instruct the subject to flip the next switch in the sequence, delivering progressively higher voltage.
When the switch was thrown, the tape recorder would play a yelp or a scream, and at higher levels, the confederate would start pounding on the wall and demanding to be set free. He was given scripted lines about having a heart condition.
After the seventh shock, he would go completely silent to give the impression he had either passed out or died. When this happened, the administrator would continue with his questions.
Getting no response from the “unconscious” confederate, the administrator told the subject to apply higher and higher shocks, up to the last, 450-volt switch, which was colored red and labeled as potentially lethal.