The epidemiology of the spread of disease through bodily fluids can easily be demonstrated using small cups of water given to several people, one of whose contains the base sodium hydroxide (NaOH) which appears no different than water itself. To simulate interaction of bodily fluids, each person exchanges the liquid in their cup with three other individuals. After the exchange, the indicator phenolthalein is added to each person's cup and the appearance of bright pink indicates that the fluid in their cup was exchanged with the "diseased" fluid containing sodium hydroxide. To complete the demonstration, hydrochloric acid is added to the bright pink cups to simulate "a cure" until the liquid turns clear again.

Explain what chemical reactions occurred, what was the indicator detecting, and why did the color go away after the addition of hydrochloric acid. How does this demonstration relate to the titration performed in the lab?